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WGL: Search pixel format with defined swap method (opengl32)

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We want to get PFD_SWAP flags as that's required to enable incremental
rendering. However, as documented on MSDN, ChoosePixelFormat ignores
PFD_SWAP flags.

We may get PFD_SWAP flags or not depending on the way the OpenGL driver
orders its pixel formats. While PFD_SWAP flags are very important for
GUI toolkits, they are best avoided by games, as most games render the
scene in its entirety on each frame. Drivers optimized for games tend
to order pixel formats with no PFD_SWAP flags first.

Se we implement our own method to select the best pixel format. We check
for usable pixel formats and assign penalties for each one, until we find
a format with 0 penalty or the sequence ends. Then the best pixel format
is selected.
This commit is contained in:
Luca Bacci 2024-07-23 16:06:52 +02:00
parent b46a900d71
commit 41b21b6634
1 changed files with 69 additions and 21 deletions
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90
gdk/win32/gdkglcontext-win32-wgl.c
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@ -349,6 +349,72 @@ done:
#undef EXT_CALL
}
static int
get_distance (PIXELFORMATDESCRIPTOR *pfd)
{
const DWORD swap_flags = PFD_SWAP_COPY | PFD_SWAP_EXCHANGE;
int is_double_buffered = (pfd->dwFlags & PFD_DOUBLEBUFFER) != 0;
int is_swap_defined = (pfd->dwFlags & swap_flags) != 0;
int is_bgra = pfd->cBlueShift == 0 && pfd->cGreenShift == 8 &&
pfd->cRedShift == 16 && pfd->cAlphaShift == 24;
int is_mono = (pfd->dwFlags & PFD_STEREO) == 0;
int ancillary_bits = pfd->cStencilBits + pfd->cDepthBits + pfd->cAccumBits;
int quality_distance = !is_double_buffered * 1000;
int performance_distance = !is_swap_defined * 200 + !is_bgra * 100;
int memory_distance = !is_mono + ancillary_bits;
return quality_distance +
performance_distance +
memory_distance;
}
/* ChoosePixelFormat ignored some fields and flags, which makes it
* less useful for GTK. In particular, it ignores the PFD_SWAP flags,
* which are very important for GUI toolkits. Here we implement an
* analog function which is tied to the needs of GTK */
static int
choose_pixel_format_opengl32 (HDC hdc)
{
const DWORD skip_flags = PFD_GENERIC_FORMAT |
PFD_GENERIC_ACCELERATED;
const DWORD required_flags = PFD_DRAW_TO_WINDOW |
PFD_SUPPORT_OPENGL;
struct {
int index;
int distance;
} best = { 0, 1, }, current;
PIXELFORMATDESCRIPTOR pfd;
int count = DescribePixelFormat (hdc, 1, sizeof (pfd), NULL);
for (current.index = 1; current.index <= count && best.distance > 0; current.index++)
{
if (DescribePixelFormat (hdc, current.index, sizeof (pfd), &pfd) <= 0)
{
WIN32_API_FAILED ("DescribePixelFormat");
return 0;
}
if ((pfd.dwFlags & skip_flags) != 0 ||
(pfd.dwFlags & required_flags) != required_flags)
continue;
if (pfd.iPixelType != PFD_TYPE_RGBA ||
(pfd.cRedBits != 8 || pfd.cGreenBits != 8 ||
pfd.cBlueBits != 8 || pfd.cAlphaBits != 8))
continue;
current.distance = get_distance (&pfd);
if (best.index == 0 || current.distance < best.distance)
best = current;
}
return best.index;
}
static int
get_wgl_pfd (HDC hdc,
PIXELFORMATDESCRIPTOR *pfd,
@ -356,8 +422,6 @@ get_wgl_pfd (HDC hdc,
{
int best_pf = 0;
pfd->nSize = sizeof (PIXELFORMATDESCRIPTOR);
if (display_win32->hasWglARBPixelFormat)
{
/* Save up the HDC and HGLRC that we are currently using, to restore back to it when we are done here */
@ -378,26 +442,10 @@ get_wgl_pfd (HDC hdc,
}
else
{
pfd->nVersion = 1;
pfd->dwFlags = PFD_SUPPORT_OPENGL | PFD_DRAW_TO_WINDOW | PFD_DOUBLEBUFFER;
pfd->iPixelType = PFD_TYPE_RGBA;
pfd->cColorBits = GetDeviceCaps (hdc, BITSPIXEL);
pfd->cAlphaBits = 8;
pfd->iLayerType = PFD_MAIN_PLANE;
pfd->cAccumBits = 0;
pfd->cStencilBits = 0;
best_pf = choose_pixel_format_opengl32 (hdc);
if (!display_win32->force_enable_depth_bits)
pfd->cDepthBits = 0;
best_pf = ChoosePixelFormat (hdc, pfd);
/* try again if driver enforces depth buffers */
if (best_pf == 0 && !display_win32->force_enable_depth_bits)
{
display_win32->force_enable_depth_bits = TRUE;
get_wgl_pfd (hdc, pfd, display_win32);
}
if (best_pf > 0)
DescribePixelFormat (hdc, best_pf, sizeof (PIXELFORMATDESCRIPTOR), pfd);
}
return best_pf;