From ed6c852102d2318f44257221d0d82b518989174e Mon Sep 17 00:00:00 2001
From: Roz K <roz@rozk.net>
Date: Thu, 29 Dec 2022 16:24:37 +0100
Subject: [PATCH] Rework GL framebuffer config selection.

---
 cpp/display/display_glx.cpp | 56 ++++++++++++++++---------------------
 1 file changed, 24 insertions(+), 32 deletions(-)

diff --git a/cpp/display/display_glx.cpp b/cpp/display/display_glx.cpp
index 2a79cc9..eb7112f 100644
--- a/cpp/display/display_glx.cpp
+++ b/cpp/display/display_glx.cpp
@@ -28,6 +28,7 @@ static bool rk_error_occured = false;
 typedef GLXContext (*rk_CreateContextAttribsFunc)(Display *, GLXFBConfig, GLXContext, Bool, int const *);
 
 static int const rk_visual_attribs[] = {
+    GLX_CONFIG_CAVEAT, GLX_NONE,
     GLX_X_RENDERABLE, True,
     GLX_DRAWABLE_TYPE, GLX_WINDOW_BIT,
     GLX_RENDER_TYPE, GLX_RGBA_BIT,
@@ -140,42 +141,33 @@ rk_display_t rk_create_display(
         return nullptr;
     }
 
-    int fbcount;
-    GLXFBConfig * const fbc = glXChooseFBConfig(
-        display->display, DefaultScreen(display->display), rk_visual_attribs, &fbcount);
-    if (!fbc) {
+    int fb_count = 0;
+    GLXFBConfig * const fb_configs = glXChooseFBConfig(
+        display->display, DefaultScreen(display->display), rk_visual_attribs, &fb_count);
+    printf("[GLX] Found %d framebuffer configs.\n", fb_count);
+    if (!fb_configs || !fb_count) {
         rk_glx_printf("Failed to retrieve framebuffer configs.");
         rk_destroy_display(reinterpret_cast<rk_display_t>(display));
         return nullptr;
     }
-    printf("[GLX] Found %d framebuffer configs.\n", fbcount);
+    GLXFBConfig const fb_config = fb_configs[0];
+    XFree(fb_configs);
+    int red_size = 0;
+    glXGetFBConfigAttrib(display->display, fb_config, GLX_RED_SIZE, &red_size);
+    int green_size = 0;
+    glXGetFBConfigAttrib(display->display, fb_config, GLX_GREEN_SIZE, &green_size);
+    int blue_size = 0;
+    glXGetFBConfigAttrib(display->display, fb_config, GLX_BLUE_SIZE, &blue_size);
+    int alpha_size = 0;
+    glXGetFBConfigAttrib(display->display, fb_config, GLX_ALPHA_SIZE, &alpha_size);
+    int depth_size = 0;
+    glXGetFBConfigAttrib(display->display, fb_config, GLX_DEPTH_SIZE, &depth_size);
+    int stencil_size = 0;
+    glXGetFBConfigAttrib(display->display, fb_config, GLX_STENCIL_SIZE, &stencil_size);
+    printf("[GLX] Select framebuffer config R%dG%dB%dA%d D%dS%d.\n",
+        red_size, green_size, blue_size, alpha_size, depth_size, stencil_size);
 
-    int best_fbc = -1;
-    int best_num_samp = -1;
-    for (int i = 0; i < fbcount; ++i) {
-        XVisualInfo * const vi = glXGetVisualFromFBConfig(display->display, fbc[i]);
-        if (vi) {
-            int samp_buf, samples;
-            glXGetFBConfigAttrib(display->display, fbc[i], GLX_SAMPLE_BUFFERS, &samp_buf);
-            glXGetFBConfigAttrib(display->display, fbc[i], GLX_SAMPLES, &samples);
-            if (best_fbc < 0 || (samp_buf && samples > best_num_samp)) {
-                best_fbc = i;
-                best_num_samp = samples;
-            }
-            XFree(vi);
-        }
-    }
-    if (best_fbc == -1) {
-        XFree(fbc);
-        rk_glx_printf("Failed to find a suitable framebuffer config.");
-        rk_destroy_display(reinterpret_cast<rk_display_t>(display));
-        return nullptr;
-    }
-    GLXFBConfig const bestFbc = fbc[best_fbc];
-    XFree(fbc);
-    printf("[GLX] Select framebuffer config with %d samples.\n", best_num_samp);
-
-    XVisualInfo * const vi = glXGetVisualFromFBConfig(display->display, bestFbc);
+    XVisualInfo * const vi = glXGetVisualFromFBConfig(display->display, fb_config);
     display->colormap = XCreateColormap(
         display->display, RootWindow(display->display, vi->screen), vi->visual, AllocNone);
     XSetWindowAttributes swa;
@@ -194,7 +186,7 @@ rk_display_t rk_create_display(
 
     rk_error_occured = false;
     int (*oldHandler)(Display *, XErrorEvent *) = XSetErrorHandler(&rk_error_handler);
-    display->context = glXCreateContextAttribs(display->display, bestFbc, 0, True, rk_context_attribs);
+    display->context = glXCreateContextAttribs(display->display, fb_config, 0, True, rk_context_attribs);
     XSync(display->display, False);
     XSetErrorHandler(oldHandler);
     if (rk_error_occured || !display->context) {