Reintroduced manual framebuffer config selection.

The default behavior of WGL, EGL and GLX is to choose a config that has /at least/ the specified number of bits, whereas the GLFW 2 behavior was to choose the closest match with very few hard constraints. Moving the responsibility of finding the supported minimum values to the client was problematic, as there's no way to enumerate supported configurations, forcing the client to perform multiple (and slow) window/context creation attempts. Not even the currently set defaults (24-bit color and depth, 8-bit stencil) is universally supported, as bug reports show.
2026-09-19 15:25:50 +00:00 · 2013-05-13 15:49:59 +02:00
parent 538556bfd5
commit d82f068f7e
9 changed files with 589 additions and 256 deletions
@@ -204,6 +204,163 @@ GLboolean _glfwIsValidContextConfig(_GLFWwndconfig* wndconfig)
    return GL_TRUE;
 }

+const _GLFWfbconfig* _glfwChooseFBConfig(const _GLFWfbconfig* desired,
+                                         const _GLFWfbconfig* alternatives,
+                                         unsigned int count)
+{
+    unsigned int i;
+    unsigned int missing, leastMissing = UINT_MAX;
+    unsigned int colorDiff, leastColorDiff = UINT_MAX;
+    unsigned int extraDiff, leastExtraDiff = UINT_MAX;
+    const _GLFWfbconfig* current;
+    const _GLFWfbconfig* closest = NULL;
+
+    for (i = 0;  i < count;  i++)
+    {
+        current = alternatives + i;
+
+        if (desired->stereo > 0 && current->stereo == 0)
+        {
+            // Stereo is a hard constraint
+            continue;
+        }
+
+        // Count number of missing buffers
+        {
+            missing = 0;
+
+            if (desired->alphaBits > 0 && current->alphaBits == 0)
+                missing++;
+
+            if (desired->depthBits > 0 && current->depthBits == 0)
+                missing++;
+
+            if (desired->stencilBits > 0 && current->stencilBits == 0)
+                missing++;
+
+            if (desired->auxBuffers > 0 && current->auxBuffers < desired->auxBuffers)
+                missing += desired->auxBuffers - current->auxBuffers;
+
+            if (desired->samples > 0 && current->samples == 0)
+            {
+                // Technically, several multisampling buffers could be
+                // involved, but that's a lower level implementation detail and
+                // not important to us here, so we count them as one
+                missing++;
+            }
+        }
+
+        // These polynomials make many small channel size differences matter
+        // less than one large channel size difference
+
+        // Calculate color channel size difference value
+        {
+            colorDiff = 0;
+
+            if (desired->redBits > 0)
+            {
+                colorDiff += (desired->redBits - current->redBits) *
+                             (desired->redBits - current->redBits);
+            }
+
+            if (desired->greenBits > 0)
+            {
+                colorDiff += (desired->greenBits - current->greenBits) *
+                             (desired->greenBits - current->greenBits);
+            }
+
+            if (desired->blueBits > 0)
+            {
+                colorDiff += (desired->blueBits - current->blueBits) *
+                             (desired->blueBits - current->blueBits);
+            }
+        }
+
+        // Calculate non-color channel size difference value
+        {
+            extraDiff = 0;
+
+            if (desired->alphaBits > 0)
+            {
+                extraDiff += (desired->alphaBits - current->alphaBits) *
+                             (desired->alphaBits - current->alphaBits);
+            }
+
+            if (desired->depthBits > 0)
+            {
+                extraDiff += (desired->depthBits - current->depthBits) *
+                             (desired->depthBits - current->depthBits);
+            }
+
+            if (desired->stencilBits > 0)
+            {
+                extraDiff += (desired->stencilBits - current->stencilBits) *
+                             (desired->stencilBits - current->stencilBits);
+            }
+
+            if (desired->accumRedBits > 0)
+            {
+                extraDiff += (desired->accumRedBits - current->accumRedBits) *
+                             (desired->accumRedBits - current->accumRedBits);
+            }
+
+            if (desired->accumGreenBits > 0)
+            {
+                extraDiff += (desired->accumGreenBits - current->accumGreenBits) *
+                             (desired->accumGreenBits - current->accumGreenBits);
+            }
+
+            if (desired->accumBlueBits > 0)
+            {
+                extraDiff += (desired->accumBlueBits - current->accumBlueBits) *
+                             (desired->accumBlueBits - current->accumBlueBits);
+            }
+
+            if (desired->accumAlphaBits > 0)
+            {
+                extraDiff += (desired->accumAlphaBits - current->accumAlphaBits) *
+                             (desired->accumAlphaBits - current->accumAlphaBits);
+            }
+
+            if (desired->samples > 0)
+            {
+                extraDiff += (desired->samples - current->samples) *
+                             (desired->samples - current->samples);
+            }
+
+            if (desired->sRGB)
+            {
+                if (!current->sRGB)
+                    extraDiff++;
+            }
+        }
+
+        // Figure out if the current one is better than the best one found so far
+        // Least number of missing buffers is the most important heuristic,
+        // then color buffer size match and lastly size match for other buffers
+
+        if (missing < leastMissing)
+            closest = current;
+        else if (missing == leastMissing)
+        {
+            if ((colorDiff < leastColorDiff) ||
+                (colorDiff == leastColorDiff && extraDiff < leastExtraDiff))
+            {
+                closest = current;
+            }
+        }
+
+        if (current == closest)
+        {
+            leastMissing = missing;
+            leastColorDiff = colorDiff;
+            leastExtraDiff = extraDiff;
+        }
+    }
+
+    return closest;
+}
+
 GLboolean _glfwRefreshContextParams(void)
 {
    _GLFWwindow* window = _glfwPlatformGetCurrentContext();