st/wgl: improve selection of pixel format

Current selection of pixel format does not enforce the request of
stencil or depth buffer if the color depth is not the same as
requested.

For instance, GLUT requests a 32-bit color buffer with an 8-bit
stencil buffer, but because color buffers are only 24-bit, no
priority is given to creating a stencil buffer.

This patch gives more priority to the creation of requested buffers
and less priority to the difference in bit depth.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=101703
Signed-off-by: Olivier Lauffenburger <[email protected]>
Tested-by: Brian Paul <[email protected]>
Reviewed-by: Brian Paul <[email protected]>

1 files changed, 29 insertions, 7 deletions

diff --git a/src/gallium/state_trackers/wgl/stw_pixelformat.c b/src/gallium/state_trackers/wgl/stw_pixelformat.c
index 7763f71cbc6..833308d964c 100644
--- a/src/gallium/state_trackers/wgl/stw_pixelformat.c
+++ b/src/gallium/state_trackers/wgl/stw_pixelformat.c
@@ -432,17 +432,39 @@ stw_pixelformat_choose(HDC hdc, CONST PIXELFORMATDESCRIPTOR *ppfd)
           !!(pfi->pfd.dwFlags & PFD_DOUBLEBUFFER))
          continue;
 
-      /* FIXME: Take in account individual channel bits */
-      if (ppfd->cColorBits != pfi->pfd.cColorBits)
-         delta += 8;
+      /* Selection logic:
+      * - Enabling a feature (depth, stencil...) is given highest priority.
+      * - Giving as many bits as requested is given medium priority.
+      * - Giving no more bits than requested is given lowest priority.
+      */
 
-      if (ppfd->cDepthBits != pfi->pfd.cDepthBits)
-         delta += 4;
+      /* FIXME: Take in account individual channel bits */
+      if (ppfd->cColorBits && !pfi->pfd.cColorBits)
+         delta += 10000;
+      else if (ppfd->cColorBits > pfi->pfd.cColorBits)
+         delta += 100;
+      else if (ppfd->cColorBits < pfi->pfd.cColorBits)
+         delta++;
 
-      if (ppfd->cStencilBits != pfi->pfd.cStencilBits)
+      if (ppfd->cDepthBits && !pfi->pfd.cDepthBits)
+         delta += 10000;
+      else if (ppfd->cDepthBits > pfi->pfd.cDepthBits)
+         delta += 200;
+      else if (ppfd->cDepthBits < pfi->pfd.cDepthBits)
          delta += 2;
 
-      if (ppfd->cAlphaBits != pfi->pfd.cAlphaBits)
+      if (ppfd->cStencilBits && !pfi->pfd.cStencilBits)
+         delta += 10000;
+      else if (ppfd->cStencilBits > pfi->pfd.cStencilBits)
+         delta += 400;
+      else if (ppfd->cStencilBits < pfi->pfd.cStencilBits)
+         delta++;
+
+      if (ppfd->cAlphaBits && !pfi->pfd.cAlphaBits)
+         delta += 10000;
+      else if (ppfd->cAlphaBits > pfi->pfd.cAlphaBits)
+         delta += 100;
+      else if (ppfd->cAlphaBits < pfi->pfd.cAlphaBits)
          delta++;
 
       if (delta < bestdelta) {