graphics: rewrite screenshot and api capture image processing (#870)

## Link to GitHub Issue or related Pull Request, if one exists
#0

## Description of change
Significantly speeds up API screen capture and D3D9 screenshots saving.
Two reasons for doing this:

1. We now have a 4K game (GITADORA) and existing capture code was taking
multiple seconds.
2. Renewed user interest on streaming as we have a couple more companion
apps in active development.

**API screen capture (streaming), 1280x720:** 14.3ms -> 6.3ms per frame.
Back buffer copies go to pooled `D3DPOOL_SYSTEMMEM` surfaces via
`GetRenderTargetData` instead of allocating a lockable render target
every frame, and TooJpeg is replaced with libjpeg-turbo (encode 9.8ms ->
3.0ms). MSAA remains unsupported

**Screenshots for GITADORA arena model, across 4 screens with one of
them 4K**: 4068ms -> 124ms. `D3DXSaveSurfaceToFileA` is replaced with
fpng (encode 4043ms -> 76ms) and the screens encode in parallel.
Dropping D3DX also removes the `d3dx9_43.dll` ... `d3dx9_24.dll` probing
loop, so screenshots no longer fail outright on machines with no D3DX9
runtime installed.

Screenshot surfaces are read on the present thread, so no D3D call
reaches another thread for screenshots. This fixes a hang in DDR X2
introduced earlier in the branch: its device has no internal locking,
and reading the surface on a pool thread while the present thread sat
inside `GetRenderTargetData` left the game's own render thread
deadlocked.


## Testing

- **GITADORA** (arena model, D3D9Ex, 4K main plus three subscreens,
windowed) with
`-screenshotsub`: three sets of four screenshots, images verified
correct. Completion
order differs between sets, so the screens really are encoding in
parallel.
- **LovePlus** (KLP, plain D3D9, 768x1360): covers the inline path used
by games whose
  image processing must not leave the present thread. 
- **API screen capture** through a companion app: live video correct
throughout.
- **Print Screen** bound as the screenshot key: the clipboard copy
succeeded on every shot.
- Quitting the game after capturing leaves no `IDirect3DDevice9`
reference count warning,
  so the pooled readback surfaces are released along with the device.

src/spice2x/hooks/graphics/backends/d3d9/d3d9_device.cpp

@@ -17,6 +17,7 @@
 
 #include "d3d9_backend.h"
 #include "d3d9_live2d.h"
+#include "d3d9_readback.h"
 #include "d3d9_texture.h"
 
 #ifndef SPICE64
@@ -156,6 +157,8 @@ ULONG STDMETHODCALLTYPE WrappedIDirect3DDevice9::Release() {
             }
         }
 
+        d3d9_readback::release_device_resources(this->pReal);
+
         if (overlay::ENABLED) {
             const std::lock_guard<std::mutex> lock(overlay::OVERLAY_MUTEX);
 

src/spice2x/hooks/graphics/backends/d3d9/d3d9_readback.cpp

@@ -0,0 +1,241 @@
+#include "d3d9_readback.h"
+
+#include <mutex>
+#include <vector>
+
+#include "hooks/graphics/graphics.h"
+#include "util/logging.h"
+
+namespace d3d9_readback {
+
+namespace {
+
+SurfacePtr create_readback_surface(IDirect3DDevice9 *device, const D3DSURFACE_DESC &desc) {
+    IDirect3DSurface9 *surface = nullptr;
+    const HRESULT hr = device->CreateOffscreenPlainSurface(
+            desc.Width, desc.Height, desc.Format, D3DPOOL_SYSTEMMEM, &surface, nullptr);
+
+    if (FAILED(hr) || surface == nullptr) {
+        log_warning("graphics::d3d9",
+                "failed to create readback surface, hr={}",
+                FMT_HRESULT(hr));
+        return nullptr;
+    }
+
+    return SurfacePtr(surface);
+}
+
+size_t surface_bytes(const D3DSURFACE_DESC &desc) {
+    size_t bytes_per_pixel = 4;
+    switch (desc.Format) {
+        case D3DFMT_R5G6B5:
+        case D3DFMT_X1R5G5B5:
+        case D3DFMT_A1R5G5B5:
+            bytes_per_pixel = 2;
+            break;
+        default:
+            break;
+    }
+
+    return static_cast<size_t>(desc.Width) * desc.Height * bytes_per_pixel;
+}
+
+// idle surfaces are kept between captures, bucketed by layout so that screens of
+// differing resolution do not evict each other. a new device drops everything,
+// since system memory surfaces outlive Reset but not the device itself
+class ReadbackPool {
+public:
+    SurfacePtr acquire(IDirect3DDevice9 *device, const D3DSURFACE_DESC &desc) {
+        {
+            std::lock_guard<std::mutex> lock(this->mutex);
+
+            if (this->device != device) {
+                this->drop();
+                this->device = device;
+            }
+
+            auto *bucket = this->find(desc);
+            if (bucket && !bucket->idle.empty()) {
+                auto surface = std::move(bucket->idle.back());
+                bucket->idle.pop_back();
+
+                const size_t bytes = surface_bytes(desc);
+                this->idle_bytes = this->idle_bytes > bytes ? this->idle_bytes - bytes : 0;
+                return surface;
+            }
+        }
+
+        return create_readback_surface(device, desc);
+    }
+
+    void release(IDirect3DDevice9 *device, SurfacePtr surface) {
+        if (!surface) {
+            return;
+        }
+
+        D3DSURFACE_DESC desc {};
+        if (FAILED(surface->GetDesc(&desc))) {
+            return;
+        }
+
+        const size_t bytes = surface_bytes(desc);
+
+        std::lock_guard<std::mutex> lock(this->mutex);
+        if (this->device != device || this->idle_bytes + bytes > MAX_IDLE_BYTES) {
+            return;
+        }
+
+        auto *bucket = this->find(desc);
+        if (bucket == nullptr) {
+            if (this->buckets.size() >= MAX_BUCKETS) {
+                return;
+            }
+
+            this->buckets.push_back(Bucket { desc.Width, desc.Height, desc.Format, {} });
+            bucket = &this->buckets.back();
+        }
+
+        if (bucket->idle.size() < MAX_IDLE_PER_BUCKET) {
+            bucket->idle.push_back(std::move(surface));
+            this->idle_bytes += bytes;
+        }
+    }
+
+    // every cached surface holds a reference on the device, so they have to go
+    // before it does or the device never reaches a zero reference count
+    void clear_device(IDirect3DDevice9 *device) {
+        std::lock_guard<std::mutex> lock(this->mutex);
+        if (this->device != device) {
+            return;
+        }
+
+        this->drop();
+        this->device = nullptr;
+    }
+
+private:
+    struct Bucket {
+        UINT width;
+        UINT height;
+        D3DFORMAT format;
+        std::vector<SurfacePtr> idle;
+    };
+
+    static constexpr size_t MAX_BUCKETS = GRAPHICS_CAPTURE_SCREEN_NO;
+
+    // one returning surface plus one for the next capture; a full screen surface
+    // is several megabytes, so the cap matters
+    static constexpr size_t MAX_IDLE_PER_BUCKET = 2;
+
+    // a 4K surface is 33MB, so the per bucket count alone does not bound this
+    static constexpr size_t MAX_IDLE_BYTES = 64u * 1024 * 1024;
+
+    void drop() {
+        this->buckets.clear();
+        this->idle_bytes = 0;
+    }
+
+    Bucket *find(const D3DSURFACE_DESC &desc) {
+        for (auto &bucket : this->buckets) {
+            if (bucket.width == desc.Width
+                    && bucket.height == desc.Height
+                    && bucket.format == desc.Format) {
+                return &bucket;
+            }
+        }
+
+        return nullptr;
+    }
+
+    std::mutex mutex;
+    std::vector<Bucket> buckets;
+    IDirect3DDevice9 *device = nullptr;
+    size_t idle_bytes = 0;
+};
+
+// deliberately never destroyed: releasing D3D surfaces during static destruction
+// would run after d3d9 may already be unloaded
+ReadbackPool &pool() {
+    static ReadbackPool *instance = new ReadbackPool();
+    return *instance;
+}
+
+} // namespace
+
+void release_device_resources(IDirect3DDevice9 *device) {
+    pool().clear_device(device);
+}
+
+BackbufferCopy::~BackbufferCopy() {
+    if (this->pooled && this->surface) {
+        pool().release(this->device, std::move(this->surface));
+    }
+}
+
+std::optional<BackbufferCopy> acquire_backbuffer_copy(
+        IDirect3DDevice9 *device, IDirect3DSwapChain9 *swap_chain, int screen, bool pooled) {
+
+    IDirect3DSurface9 *buffer = nullptr;
+    HRESULT hr = swap_chain->GetBackBuffer(0, D3DBACKBUFFER_TYPE_MONO, &buffer);
+    if (FAILED(hr) || buffer == nullptr) {
+        log_warning("graphics::d3d9",
+                "failed to get back buffer for screen {}, hr={}",
+                screen,
+                FMT_HRESULT(hr));
+        return std::nullopt;
+    }
+
+    D3DSURFACE_DESC desc {};
+    hr = buffer->GetDesc(&desc);
+    if (FAILED(hr)) {
+        log_warning("graphics::d3d9",
+                "failed to acquire back buffer descriptor, hr={}",
+                FMT_HRESULT(hr));
+        buffer->Release();
+        return std::nullopt;
+    }
+
+    // GetRenderTargetData rejects multisampled sources. no supported game has been
+    // seen presenting one, so resolving is left unimplemented rather than untested
+    if (desc.MultiSampleType != D3DMULTISAMPLE_NONE) {
+        static std::once_flag warned;
+        std::call_once(warned, [&desc] {
+            log_warning("graphics::d3d9",
+                    "back buffer is multisampled ({}), screenshots and capture are unsupported",
+                    static_cast<uint32_t>(desc.MultiSampleType));
+        });
+        buffer->Release();
+        return std::nullopt;
+    }
+
+    auto destination = pooled
+            ? pool().acquire(device, desc)
+            : create_readback_surface(device, desc);
+    if (!destination) {
+        buffer->Release();
+        return std::nullopt;
+    }
+
+    hr = device->GetRenderTargetData(buffer, destination.get());
+    buffer->Release();
+
+    if (FAILED(hr)) {
+        log_warning("graphics::d3d9",
+                "failed to copy back buffer contents, hr={}",
+                FMT_HRESULT(hr));
+        if (pooled) {
+            pool().release(device, std::move(destination));
+        }
+        return std::nullopt;
+    }
+
+    BackbufferCopy copy;
+    copy.screen = screen;
+    copy.desc = desc;
+    copy.device = device;
+    copy.surface = std::move(destination);
+    copy.pooled = pooled;
+
+    return copy;
+}
+}

src/spice2x/hooks/graphics/backends/d3d9/d3d9_readback.h

@@ -0,0 +1,44 @@
+#pragma once
+
+#include <memory>
+#include <optional>
+
+#include <d3d9.h>
+
+namespace d3d9_readback {
+
+    struct SurfaceReleaser {
+        void operator()(IDirect3DSurface9 *surface) const {
+            surface->Release();
+        }
+    };
+
+    using SurfacePtr = std::unique_ptr<IDirect3DSurface9, SurfaceReleaser>;
+
+    // system memory copy of a back buffer; locking it neither stalls the GPU nor reads over PCIe
+    struct BackbufferCopy {
+        int screen {};
+        D3DSURFACE_DESC desc {};
+        IDirect3DDevice9 *device = nullptr;
+        SurfacePtr surface;
+        bool pooled = false;
+
+        BackbufferCopy() = default;
+        BackbufferCopy(BackbufferCopy &&) noexcept = default;
+        BackbufferCopy &operator=(BackbufferCopy &&) noexcept = default;
+        BackbufferCopy(const BackbufferCopy &) = delete;
+        BackbufferCopy &operator=(const BackbufferCopy &) = delete;
+        ~BackbufferCopy();
+    };
+
+    // pooled copies reuse surfaces across calls and return them once the copy is destroyed,
+    // so the caller must keep it alive for as long as the pixels are being read
+    std::optional<BackbufferCopy> acquire_backbuffer_copy(
+            IDirect3DDevice9 *device,
+            IDirect3DSwapChain9 *swap_chain,
+            int screen,
+            bool pooled);
+
+    // pooled surfaces hold references on the device; call this before releasing it
+    void release_device_resources(IDirect3DDevice9 *device);
+}

src/spice2x/hooks/graphics/backends/d3d9/d3d9_screenshot.cpp

@@ -1,7 +1,10 @@
 #include "d3d9_screenshot.h"
 
 #include <cstdint>
+#include <cstring>
 #include <filesystem>
+#include <future>
+#include <limits>
 #include <memory>
 #include <mutex>
 #include <optional>
@@ -10,38 +13,21 @@
 #include <vector>
 
 #include <external/robin_hood.h>
-
-#ifdef __GNUC__
-#include <d3dx9tex.h>
-#endif
+#include <external/fpng/fpng.h>
 
 #include "avs/game.h"
 #include "hooks/graphics/graphics.h"
 #include "misc/clipboard.h"
 #include "overlay/notifications.h"
 #include "util/fileutils.h"
-#include "util/libutils.h"
 #include "util/logging.h"
 #include "util/threadpool.h"
 
 #include "d3d9_device.h"
+#include "d3d9_readback.h"
 
-#ifdef __GNUC__
-typedef decltype(D3DXSaveSurfaceToFileA) *D3DXSaveSurfaceToFileA_t;
-#else
-#define D3DXIFF_PNG ((DWORD) 3)
-
-typedef HRESULT (WINAPI *D3DXSaveSurfaceToFileA_t)(
-        LPCSTR pDestFile,
-        DWORD DestFormat,
-        LPDIRECT3DSURFACE9 pSrcSurface,
-        CONST PALETTEENTRY *pSrcPalette,
-        CONST RECT *pSrcRect);
-#endif
-
-static bool ATTEMPTED_D3DX9_LOAD_LIBRARY = false;
-
-// genpath picks free filenames by probing the disk, so only one save may run at a time
+// genpath picks filenames by probing the disk, so the whole save has to be serialised:
+// a name is only taken once its file exists, not when genpath hands it out
 static std::mutex SCREENSHOT_SAVE_M;
 
 namespace {
@@ -56,56 +42,146 @@ struct ImageRequest {
     int screen;
 };
 
-struct SurfaceReleaser {
-    void operator()(IDirect3DSurface9 *surface) const {
-        surface->Release();
-    }
-};
-
-using SurfacePtr = std::unique_ptr<IDirect3DSurface9, SurfaceReleaser>;
-
-struct BackbufferCopy {
+// a screen already read out of its surface, so nothing here touches D3D. the bytes
+// are still in the surface's format; converting them is left to the encode
+struct PendingWrite {
     int screen {};
-    D3DSURFACE_DESC desc {};
-    SurfacePtr surface;
+    D3DFORMAT format {};
+    UINT width {};
+    UINT height {};
+    size_t pitch {};
+    std::vector<uint8_t> data;
+    std::string path;
+    bool saved = false;
 };
 
-} // namespace
+struct PendingCapture {
+    int screen {};
+    D3DFORMAT format {};
+    UINT width {};
+    UINT height {};
+    size_t pitch {};
+    std::vector<uint8_t> data;
+};
 
-static void save_capture(
-        int screen,
+// packed 24bpp RGB, what both the png encoder and the api capture consume
+constexpr size_t RGB_PIXEL_SIZE = 3;
+
+// the formats surface_to_rgb knows how to convert; the two must stay in sync
+static std::optional<size_t> surface_pixel_size(D3DFORMAT format) {
+    switch (format) {
+        // what back buffers are actually created as in practice
+        case D3DFMT_X8R8G8B8:
+        case D3DFMT_A8R8G8B8:
+
+        // a valid display format, but no supported game has been seen presenting one
+        case D3DFMT_A2R10G10B10:
+            return 4;
+
+        // valid display formats, but no supported game has been seen presenting one
+        case D3DFMT_R5G6B5:
+        case D3DFMT_X1R5G5B5:
+        case D3DFMT_A1R5G5B5:
+            return 2;
+
+        default:
+            return std::nullopt;
+    }
+}
+
+struct ImageSize {
+    size_t row_size {};
+    size_t total_size {};
+};
+
+static std::optional<ImageSize> compute_image_size(
+        UINT width,
+        UINT height,
+        size_t bytes_per_pixel) {
+
+    if (width == 0 || height == 0
+            || width > std::numeric_limits<size_t>::max() / bytes_per_pixel) {
+        return std::nullopt;
+    }
+
+    const size_t row_size = static_cast<size_t>(width) * bytes_per_pixel;
+    if (height > std::numeric_limits<size_t>::max() / row_size) {
+        return std::nullopt;
+    }
+
+    return ImageSize { row_size, static_cast<size_t>(height) * row_size };
+}
+
+static bool resize_pixels(std::vector<uint8_t> &pixels, size_t size) {
+    try {
+        pixels.resize(size);
+        return true;
+    } catch (const std::exception &error) {
+        log_warning("graphics::d3d9", "failed to allocate image buffer: {}", error.what());
+        return false;
+    }
+}
+
+// the api capture stages a whole back buffer every frame, so the staging buffer
+// is recycled rather than reallocated. returned buffers keep their size, which
+// leaves the reuse free of a zero fill
+class CaptureBuffers {
+public:
+    std::vector<uint8_t> take() {
+        std::lock_guard<std::mutex> lock(this->mutex);
+        if (this->idle.empty()) {
+            return {};
+        }
+
+        auto buffer = std::move(this->idle.back());
+        this->idle.pop_back();
+        return buffer;
+    }
+
+    void give(std::vector<uint8_t> buffer) {
+        std::lock_guard<std::mutex> lock(this->mutex);
+        if (this->idle.size() < MAX_IDLE) {
+            this->idle.push_back(std::move(buffer));
+        }
+    }
+
+private:
+    // one per save in flight plus one for the next capture; a full screen is
+    // several megabytes, so the cap matters
+    static constexpr size_t MAX_IDLE = 2;
+
+    std::mutex mutex;
+    std::vector<std::vector<uint8_t>> idle;
+};
+
+// deliberately never destroyed, so a save still running at process exit cannot
+// hand a buffer back to a dead free list
+CaptureBuffers &capture_buffers() {
+    static CaptureBuffers *instance = new CaptureBuffers();
+    return *instance;
+}
+
+// encodes get their own pool: the dispatch below already occupies a worker on its
+// pool, so queueing onto that one and waiting could starve itself. never destroyed
+// for the same reason as the buffers above
+ThreadPool &encode_pool() {
+    static auto *instance = new ThreadPool(2);
+    return *instance;
+}
+
+// normalize the supported D3D formats to packed 24bpp RGB. callers screen the
+// format through surface_pixel_size first, so the black fill below is a fallback
+void surface_to_rgb(
         D3DFORMAT format,
         UINT width,
         UINT height,
-        IDirect3DSurface9 *surface) {
-    HRESULT hr;
+        const uint8_t *data,
+        size_t pitch,
+        uint8_t *pixels) {
 
-    // lock surface to be able to access the data
-    D3DLOCKED_RECT finished_copy {};
-    hr = surface->LockRect(&finished_copy, nullptr, 0);
-    if (FAILED(hr)) {
-        log_warning("graphics::d3d9", "failed to lock screenshot surface, hr={}", FMT_HRESULT(hr));
-        graphics_capture_skip(screen);
-        return;
-    }
-
-    // normalize supported D3D formats to packed RGB for API capture
-    size_t pitch = finished_copy.Pitch;
-    auto data = reinterpret_cast<uint8_t *>(finished_copy.pBits);
-    auto pixels = std::unique_ptr<uint8_t[]>(new uint8_t[width * height * 3]);
     for (size_t row = 0; row < height; row++) {
         size_t offset_row = row * width * 3;
         switch (format) {
-            case D3DFMT_R8G8B8: {
-                for (size_t column = 0; column < width; column++) {
-                    auto cell = data + row * pitch + column * 3;
-                    auto pixel = &pixels[offset_row + column * 3];
-                    pixel[0] = cell[0];
-                    pixel[1] = cell[1];
-                    pixel[2] = cell[2];
-                }
-                break;
-            }
             case D3DFMT_X8R8G8B8:
             case D3DFMT_A8R8G8B8: {
                 for (size_t column = 0; column < width; column++) {
@@ -117,14 +193,45 @@ static void save_capture(
                 }
                 break;
             }
-            case D3DFMT_X8B8G8R8:
-            case D3DFMT_A8B8G8R8: {
+            // the 5 and 6 bit channels are widened by bit replication so that
+            // full scale stays full scale
+            case D3DFMT_R5G6B5: {
+                auto cells = reinterpret_cast<const uint16_t *>(data + row * pitch);
                 for (size_t column = 0; column < width; column++) {
-                    auto cell = data + row * pitch + column * 4;
+                    const uint16_t cell = cells[column];
+                    const uint8_t red = (cell >> 11) & 0x1F;
+                    const uint8_t green = (cell >> 5) & 0x3F;
+                    const uint8_t blue = cell & 0x1F;
                     auto pixel = &pixels[offset_row + column * 3];
-                    pixel[0] = cell[0];
-                    pixel[1] = cell[1];
-                    pixel[2] = cell[2];
+                    pixel[0] = (red << 3) | (red >> 2);
+                    pixel[1] = (green << 2) | (green >> 4);
+                    pixel[2] = (blue << 3) | (blue >> 2);
+                }
+                break;
+            }
+            case D3DFMT_X1R5G5B5:
+            case D3DFMT_A1R5G5B5: {
+                auto cells = reinterpret_cast<const uint16_t *>(data + row * pitch);
+                for (size_t column = 0; column < width; column++) {
+                    const uint16_t cell = cells[column];
+                    const uint8_t red = (cell >> 10) & 0x1F;
+                    const uint8_t green = (cell >> 5) & 0x1F;
+                    const uint8_t blue = cell & 0x1F;
+                    auto pixel = &pixels[offset_row + column * 3];
+                    pixel[0] = (red << 3) | (red >> 2);
+                    pixel[1] = (green << 3) | (green >> 2);
+                    pixel[2] = (blue << 3) | (blue >> 2);
+                }
+                break;
+            }
+            case D3DFMT_A2R10G10B10: {
+                auto cells = reinterpret_cast<const uint32_t *>(data + row * pitch);
+                for (size_t column = 0; column < width; column++) {
+                    const uint32_t cell = cells[column];
+                    auto pixel = &pixels[offset_row + column * 3];
+                    pixel[0] = static_cast<uint8_t>((cell >> 22) & 0xFF);
+                    pixel[1] = static_cast<uint8_t>((cell >> 12) & 0xFF);
+                    pixel[2] = static_cast<uint8_t>((cell >> 2) & 0xFF);
                 }
                 break;
             }
@@ -138,99 +245,148 @@ static void save_capture(
             }
         }
     }
+}
 
-    // unlock surface
-    hr = surface->UnlockRect();
-    if (FAILED(hr)) {
-        log_warning("graphics::d3d9", "failed to unlock screenshot surface, hr={}", FMT_HRESULT(hr));
-        graphics_capture_skip(screen);
+} // namespace
+
+using d3d9_readback::BackbufferCopy;
+
+static void save_capture(PendingCapture capture) {
+    const auto size = compute_image_size(capture.width, capture.height, RGB_PIXEL_SIZE);
+    if (!size.has_value()) {
+        capture_buffers().give(std::move(capture.data));
+        graphics_capture_skip(capture.screen);
         return;
     }
 
-    // enqueue
-    graphics_capture_enqueue(screen, pixels.release(), width, height);
+    auto pixels = std::unique_ptr<uint8_t[]>(new (std::nothrow) uint8_t[size->total_size]);
+    if (!pixels) {
+        log_warning("graphics::d3d9", "failed to allocate capture image buffer");
+        capture_buffers().give(std::move(capture.data));
+        graphics_capture_skip(capture.screen);
+        return;
+    }
+
+    // a format we cannot read still has to produce a frame, or api clients stall
+    if (capture.data.empty()) {
+        std::memset(pixels.get(), 0, size->total_size);
+    } else {
+        surface_to_rgb(
+                capture.format,
+                capture.width,
+                capture.height,
+                capture.data.data(),
+                capture.pitch,
+                pixels.get());
+
+        capture_buffers().give(std::move(capture.data));
+    }
+
+    graphics_capture_enqueue(capture.screen, pixels.release(), capture.width, capture.height);
 }
 
-static bool save_screenshot(
+enum class SurfaceRead {
+    Ok,
+    Unsupported,
+    Failed,
+};
+
+// copying the surface touches D3D, so it stays on the caller's thread. the bytes come
+// out in the surface's own format; converting them is plain memory work for later
+static SurfaceRead read_surface_raw(
+        const BackbufferCopy &copy,
+        size_t &row_size,
+        std::vector<uint8_t> &out) {
+
+    const auto bytes_per_pixel = surface_pixel_size(copy.desc.Format);
+    if (!bytes_per_pixel.has_value()) {
+        static std::once_flag warned;
+        std::call_once(warned, [&copy] {
+            log_warning("graphics::d3d9",
+                    "unsupported surface format {}",
+                    static_cast<uint32_t>(copy.desc.Format));
+        });
+        return SurfaceRead::Unsupported;
+    }
+
+    const auto size = compute_image_size(copy.desc.Width, copy.desc.Height, *bytes_per_pixel);
+    if (!size.has_value() || !resize_pixels(out, size->total_size)) {
+        return SurfaceRead::Failed;
+    }
+
+    D3DLOCKED_RECT locked {};
+    HRESULT hr = copy.surface->LockRect(&locked, nullptr, D3DLOCK_READONLY);
+    if (FAILED(hr)) {
+        log_warning("graphics::d3d9", "failed to lock capture surface, hr={}", FMT_HRESULT(hr));
+        return SurfaceRead::Failed;
+    }
+
+    if (locked.Pitch < 0 || static_cast<size_t>(locked.Pitch) < size->row_size) {
+        log_warning("graphics::d3d9", "capture surface has invalid pitch {}", locked.Pitch);
+        copy.surface->UnlockRect();
+        return SurfaceRead::Failed;
+    }
+
+    auto data = reinterpret_cast<const uint8_t *>(locked.pBits);
+    for (size_t row = 0; row < copy.desc.Height; row++) {
+        std::memcpy(
+                out.data() + row * size->row_size,
+                data + row * locked.Pitch,
+                size->row_size);
+    }
+
+    hr = copy.surface->UnlockRect();
+    if (FAILED(hr)) {
+        log_warning("graphics::d3d9", "failed to unlock capture surface, hr={}", FMT_HRESULT(hr));
+        return SurfaceRead::Failed;
+    }
+
+    row_size = size->row_size;
+    return SurfaceRead::Ok;
+}
+
+static bool read_capture_surface(
+        const BackbufferCopy &copy,
+        PendingCapture &capture) {
+
+    capture.screen = copy.screen;
+    capture.format = copy.desc.Format;
+    capture.width = copy.desc.Width;
+    capture.height = copy.desc.Height;
+
+    capture.data = capture_buffers().take();
+    const auto result = read_surface_raw(copy, capture.pitch, capture.data);
+    if (result == SurfaceRead::Ok) {
+        return true;
+    }
+
+    capture_buffers().give(std::move(capture.data));
+    capture.data.clear();
+
+    // a format we cannot read is reported as a black frame rather than nothing,
+    // so a client polling the api keeps getting responses
+    return result == SurfaceRead::Unsupported;
+}
+
+static bool write_screenshot_png(
         const std::string &file_path,
-        D3DFORMAT format,
         UINT width,
         UINT height,
-        IDirect3DSurface9 *surface) {
-    // 32-bit XRGB and ARGB surfaces use byte 3 as alpha; force opaque PNG output
-    if (format == D3DFMT_X8R8G8B8 || format == D3DFMT_A8R8G8B8 ||
-        format == D3DFMT_X8B8G8R8 || format == D3DFMT_A8B8G8R8) {
+        const std::vector<uint8_t> &pixels) {
 
-        D3DLOCKED_RECT finished_copy {};
-        HRESULT hr = surface->LockRect(&finished_copy, nullptr, 0);
-        if (FAILED(hr)) {
-            log_warning("graphics::d3d9", "failed to lock screenshot surface, hr={}", FMT_HRESULT(hr));
-            return false;
-        }
+    // a no-op while FPNG_NO_SSE is set, but fpng requires it before any encode
+    static std::once_flag fpng_ready;
+    std::call_once(fpng_ready, [] { fpng::fpng_init(); });
 
-        const size_t pitch = finished_copy.Pitch;
-        auto data = reinterpret_cast<uint8_t *>(finished_copy.pBits);
-        for (size_t row = 0; row < height; row++) {
-            for (size_t column = 0; column < width; column++) {
-                data[row * pitch + column * 4 + 3] = 255;
-            }
-        }
-
-        hr = surface->UnlockRect();
-        if (FAILED(hr)) {
-            log_warning("graphics::d3d9", "failed to unlock screenshot surface, hr={}", FMT_HRESULT(hr));
-            return false;
-        }
-    }
-
-    // lazy load function
-    static D3DXSaveSurfaceToFileA_t D3DXSaveSurfaceToFileA_ptr = nullptr;
-    if (D3DXSaveSurfaceToFileA_ptr == nullptr) {
-        D3DXSaveSurfaceToFileA_ptr = libutils::try_proc<D3DXSaveSurfaceToFileA_t>("D3DXSaveSurfaceToFileA");
-
-        // check if function was not found, likely because d3dx9 is not loaded
-        if (!ATTEMPTED_D3DX9_LOAD_LIBRARY && D3DXSaveSurfaceToFileA_ptr == nullptr) {
-            ATTEMPTED_D3DX9_LOAD_LIBRARY = true;
-
-            // prefer the newest installed helper while supporting older D3DX9 runtimes
-            for (size_t i = 43; i >= 24; i--) {
-                auto lib_name = fmt::format("d3dx9_{}.dll", i);
-                auto d3dx9 = libutils::try_library(lib_name);
-
-                // Check if library was not found
-                if (d3dx9 == nullptr) {
-                    continue;
-                }
-
-                D3DXSaveSurfaceToFileA_ptr = libutils::try_proc<D3DXSaveSurfaceToFileA_t>(
-                        d3dx9, "D3DXSaveSurfaceToFileA");
-
-                // Check if function was not found
-                if (D3DXSaveSurfaceToFileA_ptr == nullptr) {
-                    FreeLibrary(d3dx9);
-                    d3dx9 = nullptr;
-
-                    continue;
-                }
-
-                log_info("graphics::d3d9", "found surface save function in '{}'", lib_name);
-                break;
-            }
-        }
-    }
-
-    if (D3DXSaveSurfaceToFileA_ptr == nullptr) {
-        log_warning("graphics::d3d9", "Direct3D save helper function not available");
-        return false;
-    }
-
-    // save to file
     log_info("graphics::d3d9", "saving screenshot to {}", file_path);
-    const HRESULT save_result = D3DXSaveSurfaceToFileA_ptr(
-        file_path.c_str(), D3DXIFF_PNG, surface, nullptr, nullptr);
 
-    if (FAILED(save_result)) {
-        log_warning("graphics::d3d9", "Failed to save screenshot");
+    if (!fpng::fpng_encode_image_to_file(
+            file_path.c_str(),
+            pixels.data(),
+            static_cast<uint32_t>(width),
+            static_cast<uint32_t>(height),
+            3)) {
+        log_warning("graphics::d3d9", "failed to write screenshot png");
         return false;
     }
 
@@ -249,139 +405,9 @@ static std::string screenshot_path_for_screen(const std::string &primary_path, i
             .string();
 }
 
-static std::optional<BackbufferCopy> acquire_backbuffer_copy(
-    IDirect3DDevice9 *device, IDirect3DSwapChain9 *swap_chain, int screen) {
-
-    IDirect3DSurface9 *buffer = nullptr;
-    HRESULT hr = swap_chain->GetBackBuffer(0, D3DBACKBUFFER_TYPE_MONO, &buffer);
-    if (FAILED(hr) || buffer == nullptr) {
-        log_warning("graphics::d3d9",
-                "failed to get back buffer for screen {}, hr={}",
-                screen,
-                FMT_HRESULT(hr));
-        return std::nullopt;
-    }
-
-    D3DSURFACE_DESC desc {};
-    hr = buffer->GetDesc(&desc);
-    if (FAILED(hr)) {
-        log_warning("graphics::d3d9",
-                "failed to acquire back buffer descriptor, hr={}",
-                FMT_HRESULT(hr));
-        buffer->Release();
-        return std::nullopt;
-    }
-
-    // TODO: cache render targets
-    IDirect3DSurface9 *temp_surface = nullptr;
-    hr = device->CreateRenderTarget(
-            desc.Width, desc.Height, desc.Format, desc.MultiSampleType,
-            desc.MultiSampleQuality, TRUE, &temp_surface, nullptr);
-    if (FAILED(hr) || temp_surface == nullptr) {
-        log_warning("graphics::d3d9",
-                "failed to acquire temporary surface, hr={}",
-                FMT_HRESULT(hr));
-        buffer->Release();
-        return std::nullopt;
-    }
-
-    hr = device->StretchRect(buffer, nullptr, temp_surface, nullptr, D3DTEXF_NONE);
-    if (FAILED(hr)) {
-        log_warning("graphics::d3d9",
-                "failed to copy back buffer contents, hr={}",
-                FMT_HRESULT(hr));
-        temp_surface->Release();
-        buffer->Release();
-        return std::nullopt;
-    }
-
-    // release original back buffer reference
-    buffer->Release();
-
-    return BackbufferCopy {
-        .screen = screen,
-        .desc = desc,
-        .surface = SurfacePtr(temp_surface),
-    };
-}
-
-static void dispatch_surface_save(
-        const ImageRequest &request,
-        std::vector<BackbufferCopy> copies,
-        size_t screen_count) {
-    auto surface_process = [request, screen_count, copies = std::move(copies)]() {
-        switch (request.kind) {
-            case ImageRequestKind::Capture: {
-                const auto &copy = copies.front();
-                save_capture(
-                        request.screen,
-                        copy.desc.Format,
-                        copy.desc.Width,
-                        copy.desc.Height,
-                        copy.surface.get());
-                break;
-            }
-
-            case ImageRequestKind::Screenshot: {
-                std::lock_guard<std::mutex> lock(SCREENSHOT_SAVE_M);
-
-                std::vector<int> screens;
-                screens.reserve(copies.size());
-                for (const auto &copy : copies) {
-                    screens.push_back(copy.screen);
-                }
-
-                const auto base_path = graphics_screenshot_genpath(screens);
-                if (base_path.empty()) {
-                    break;
-                }
-
-                // screens missing from copies already failed to be acquired
-                size_t failed = screen_count - copies.size();
-                std::string primary_path;
-                std::string notify_path;
-                for (const auto &copy : copies) {
-                    const auto path = screenshot_path_for_screen(base_path, copy.screen);
-                    if (!save_screenshot(
-                            path,
-                            copy.desc.Format,
-                            copy.desc.Width,
-                            copy.desc.Height,
-                            copy.surface.get())) {
-                        failed++;
-                        continue;
-                    }
-                    if (notify_path.empty()) {
-                        notify_path = path;
-                    }
-                    if (copy.screen == 0) {
-                        primary_path = path;
-                    }
-                }
-
-                // only the primary screen goes to the clipboard, but any saved file is a success
-                if (!primary_path.empty()) {
-                    clipboard::copy_image(primary_path);
-                }
-                if (!notify_path.empty()) {
-                    overlay::notifications::add(
-                        overlay::notifications::Severity::Success,
-                        fmt::format("Screenshot saved: {}", fileutils::basename(notify_path)));
-                } else {
-                    overlay::notifications::add(
-                        overlay::notifications::Severity::Error,
-                        "Screenshot failed to save");
-                }
-
-                if (failed > 0) {
-                    log_warning("graphics::d3d9", "{} screenshot screen(s) missing", failed);
-                }
-                break;
-            }
-        }
-    };
-
-    // list of games that crash when running the screenshot processor on another thread
+// games that crash or hang when the screenshot processor runs on another thread.
+// D3DCREATE_MULTITHREADED is not a predictor of this; MDX omits it and threads fine
+static bool image_processing_must_be_inline() {
     static const robin_hood::unordered_set<std::string> THREAD_BAN {
             "JMA",
 #ifndef SPICE64
@@ -393,12 +419,164 @@ static void dispatch_surface_save(
             "LMA",
     };
 
-    // run the save operation on another thread for supported games
-    if (THREAD_BAN.contains(avs::game::MODEL)) {
-        surface_process();
+    return THREAD_BAN.contains(avs::game::MODEL);
+}
+
+static void dispatch_capture_save(PendingCapture capture) {
+    auto capture_process = [capture = std::move(capture)]() mutable {
+        // an escape from here would cross a thread boundary and terminate
+        try {
+            save_capture(std::move(capture));
+        } catch (const std::exception &error) {
+            log_warning("graphics::d3d9", "capture save failed: {}", error.what());
+        } catch (...) {
+            log_warning("graphics::d3d9", "capture save failed");
+        }
+    };
+
+    if (image_processing_must_be_inline()) {
+        capture_process();
     } else {
         static auto pool = ThreadPool(2);
-        pool.add(std::move(surface_process));
+        pool.add(std::move(capture_process));
+    }
+}
+
+// by this point the pixels are plain memory, so none of this needs the device
+static void dispatch_screenshot_save(std::vector<PendingWrite> writes, size_t screen_count) {
+    auto screenshot_process = [writes = std::move(writes), screen_count]() mutable {
+        std::lock_guard<std::mutex> lock(SCREENSHOT_SAVE_M);
+
+        std::vector<int> screens;
+        screens.reserve(writes.size());
+        for (const auto &write : writes) {
+            screens.push_back(write.screen);
+        }
+
+        const auto base_path = graphics_screenshot_genpath(screens);
+        if (base_path.empty()) {
+            return;
+        }
+
+        for (auto &write : writes) {
+            write.path = screenshot_path_for_screen(base_path, write.screen);
+        }
+
+        // screens missing from writes either failed to be acquired or failed to read
+        size_t failed = screen_count - writes.size();
+
+        // a throw here would otherwise reach a thread boundary and terminate
+        auto encode_one = [](PendingWrite &write) {
+            try {
+                const auto rgb = compute_image_size(write.width, write.height, RGB_PIXEL_SIZE);
+                std::vector<uint8_t> pixels;
+                if (!rgb.has_value() || !resize_pixels(pixels, rgb->total_size)) {
+                    write.saved = false;
+                    return;
+                }
+
+                surface_to_rgb(
+                        write.format,
+                        write.width,
+                        write.height,
+                        write.data.data(),
+                        write.pitch,
+                        pixels.data());
+
+                // the encode below is the long part; the raw copy is dead by now
+                write.data.clear();
+                write.data.shrink_to_fit();
+
+                write.saved = write_screenshot_png(
+                        write.path, write.width, write.height, pixels);
+            } catch (const std::exception &error) {
+                log_warning("graphics::d3d9",
+                        "screenshot encode failed for {}: {}", write.path, error.what());
+                write.saved = false;
+            } catch (...) {
+                log_warning("graphics::d3d9",
+                        "screenshot encode failed for {}", write.path);
+                write.saved = false;
+            }
+        };
+
+        {
+            // sized up front and assigned by index: storing a future must not be able
+            // to throw once its task is queued, or the screen would encode twice
+            std::vector<std::future<void>> pending(writes.empty() ? 0 : writes.size() - 1);
+            for (size_t i = 1; i < writes.size(); i++) {
+                try {
+                    pending[i - 1] = encode_pool().add([&writes, &encode_one, i] {
+                        encode_one(writes[i]);
+                    });
+                } catch (const std::exception &) {
+                    // nothing to queue onto; encoding it here still makes progress
+                    encode_one(writes[i]);
+                }
+            }
+
+            if (!writes.empty()) {
+                encode_one(writes.front());
+            }
+
+            for (auto &task : pending) {
+                if (task.valid()) {
+                    task.wait();
+                }
+            }
+        }
+
+        std::string primary_path;
+        std::string notify_path;
+        for (const auto &write : writes) {
+            if (!write.saved) {
+                failed++;
+                continue;
+            }
+            if (notify_path.empty()) {
+                notify_path = write.path;
+            }
+            if (write.screen == 0) {
+                primary_path = write.path;
+            }
+        }
+
+        // only the primary screen goes to the clipboard, but any saved file is a success
+        if (!primary_path.empty()) {
+            clipboard::copy_image(primary_path);
+        }
+        if (!notify_path.empty()) {
+            overlay::notifications::add(
+                overlay::notifications::Severity::Success,
+                fmt::format("Screenshot saved: {}", fileutils::basename(notify_path)));
+        } else {
+            overlay::notifications::add(
+                overlay::notifications::Severity::Error,
+                "Screenshot failed to save");
+        }
+
+        if (failed > 0) {
+            log_warning("graphics::d3d9", "{} screenshot screen(s) missing", failed);
+        }
+    };
+
+    // genpath and the path building below allocate, so an escape from here would
+    // cross a thread boundary and terminate
+    auto guarded = [process = std::move(screenshot_process)]() mutable {
+        try {
+            process();
+        } catch (const std::exception &error) {
+            log_warning("graphics::d3d9", "screenshot save failed: {}", error.what());
+        } catch (...) {
+            log_warning("graphics::d3d9", "screenshot save failed");
+        }
+    };
+
+    if (image_processing_must_be_inline()) {
+        guarded();
+    } else {
+        static auto pool = ThreadPool(2);
+        pool.add(std::move(guarded));
     }
 }
 
@@ -427,7 +605,8 @@ static void process_image_request(
                     screen,
                     FMT_HRESULT(hr));
         } else {
-            copy = acquire_backbuffer_copy(device, swap_chain, screen);
+            // only the API capture path runs often enough to benefit from pooling
+            copy = d3d9_readback::acquire_backbuffer_copy(device, swap_chain, screen, !screenshot);
             swap_chain->Release();
         }
 
@@ -443,7 +622,39 @@ static void process_image_request(
         return;
     }
 
-    dispatch_surface_save(request, std::move(copies), screens.size());
+    if (!screenshot) {
+        PendingCapture capture;
+        if (!read_capture_surface(copies.front(), capture)) {
+            graphics_capture_skip(request.screen);
+            return;
+        }
+
+        copies.clear();
+        dispatch_capture_save(std::move(capture));
+        return;
+    }
+
+    // reading a surface touches the device, and doing that off the present thread
+    // has been seen to deadlock games whose device has no internal locking
+    std::vector<PendingWrite> writes;
+    writes.reserve(copies.size());
+    for (const auto &copy : copies) {
+        PendingWrite write;
+        write.screen = copy.screen;
+        write.format = copy.desc.Format;
+        write.width = copy.desc.Width;
+        write.height = copy.desc.Height;
+
+        if (read_surface_raw(copy, write.pitch, write.data) != SurfaceRead::Ok) {
+            continue;
+        }
+
+        writes.push_back(std::move(write));
+    }
+
+    copies.clear();
+
+    dispatch_screenshot_save(std::move(writes), screens.size());
 }
 
 void graphics_d3d9_process_screenshot(