Mesa (master): st/wgl: improve selection of pixel format

[Brian Paul]

Module: Mesa
Branch: master
Commit: 80c6598cdba36edb43d618f97175103e560d61a1
URL:    http://cgit.freedesktop.org/mesa/mesa/commit/?id=80c6598cdba36edb43d618f97175103e560d61a1

Author: Olivier Lauffenburger <o.lauffenburger at topsolid.com>
Date:   Thu Jul  6 09:08:00 2017 -0600

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 <o.lauffenburger at topsolid.com>
Tested-by: Brian Paul <brianp at vmware.com>
Reviewed-by: Brian Paul <brianp at vmware.com>

---

 src/gallium/state_trackers/wgl/stw_pixelformat.c | 36 +++++++++++++++++++-----
 1 file 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 7763f71cbc..833308d964 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) {