[PATCH v2 0/1] MR5687: ddraw: Set dwMaxVertexCount to 2048.

[Stefan Dösinger (＠stefan)]

Wine-Bug: https://bugs.winehq.org/show_bug.cgi?id=44863

The bug has been fixed already by moving ddraw4 vertex buffers into
system memory. Changing this value makes the game create a smaller
buffer, which makes the game fast on video memory buffers. I think we
should stay close to what Windows drivers report even though we
mitigated the original issue in a different way.

--
  v2: ddraw: Set dwMaxVertexCount to 2048.

https://gitlab.winehq.org/wine/wine/-/merge_requests/5687

[PATCH v2 1/1] ddraw: Set dwMaxVertexCount to 2048.

[Stefan Dösinger]

From: Stefan Dösinger

Wine-Bug: https://bugs.winehq.org/show_bug.cgi?id=44863

The bug has been fixed already by moving ddraw4 vertex buffers into
system memory. Changing this value makes the game create a smaller
buffer, which makes the game fast on video memory buffers. I think we
should stay close to what Windows drivers report even though we
mitigated the original issue in a different way.
---
 dlls/ddraw/ddraw.c | 30 +++++++++++++++++++++++++++++-
 1 file changed, 29 insertions(+), 1 deletion(-)

diff --git a/dlls/ddraw/ddraw.c b/dlls/ddraw/ddraw.c
index 5cea4677439..ed342bfd708 100644
--- a/dlls/ddraw/ddraw.c
+++ b/dlls/ddraw/ddraw.c
@@ -1231,8 +1231,36 @@ void ddraw_d3dcaps1_from_7(D3DDEVICEDESC *caps1, D3DDEVICEDESC7 *caps7)
     caps1->dpcTriCaps = caps7->dpcTriCaps;
     caps1->dwDeviceRenderBitDepth = caps7->dwDeviceRenderBitDepth;
     caps1->dwDeviceZBufferBitDepth = caps7->dwDeviceZBufferBitDepth;
+
+    /* This value is zero on all Windows drivers we have seen so far. */
     caps1->dwMaxBufferSize = 0;
-    caps1->dwMaxVertexCount = 65536;
+
+    /* AMD GPUs on Windows XP and newer report 1024 for HAL devices.
+     * Nvidia GPUs report 65534. On Windows 9x we have seen 2048 on
+     * AMD cards and 32768 on Nvidia. The API defined limit is 65536
+     * because ddraw only supports 16 bit indices.
+     *
+     * Some games, for example Prince of Persia 3D (bug 44863), create a
+     * vertex buffer to hold as many vertices as we report here. The
+     * game requests a video memory buffer, maps it, writes a handful
+     * of vertices and draws. Because IDirect3DVertexBuffer::Lock does
+     * not allow passing a range, and prior to d3d7 doesn't support
+     * NOOVERWRITE/DISCARD, the upload becomes slow if the buffer is too
+     * large. So we don't want to report a value that's too high here.
+     *
+     * Why 2048? Windows 9x was the contemporaneous system when d3d 1-4
+     * titles were written.
+     *
+     * Regardless of this value, we put ddraw4 vertex buffers into
+     * system memory because games are using them poorly. This mitigates
+     * negative effects of a large vertex count.
+     *
+     * Windows doesn't enforce this limit. A larger vertex buffer can
+     * be created and used in draws. More vertices than dwMaxVertexCount
+     * can be rendered in one draw call. SetExecuteData with a vertex
+     * count exceeding dwMaxVertexCount succeeds too. */
+    caps1->dwMaxVertexCount = 2048;
+
     caps1->dwMinTextureWidth  = caps7->dwMinTextureWidth;
     caps1->dwMinTextureHeight = caps7->dwMinTextureHeight;
     caps1->dwMaxTextureWidth  = caps7->dwMaxTextureWidth;

[Stefan Dösinger (＠stefan)]

I've pushed an updated patch that sets dwMaxVertexCount=2048 but drops the tests (because Windows turns out to be all over the place). I've done some more ad-hoc testing with dwVertexCount in SetExecuteData and found that Windows doesn't enforce the limit (neither do we).

[PATCH v2 0/1] MR5687: ddraw: Set dwMaxVertexCount to 2048. - approved

[Elizabeth Figura (＠zfigura)]

This merge request was approved by Elizabeth Figura.