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tests/games: sdl-fbo-blit in a fullscreen window

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A third argument opens the window fullscreen (SDL_WINDOW_FULLSCREEN, as
Half-Life does by default) or fullscreen-desktop; the scene then draws at
the drawable size, read every frame, into a texture big enough for any
size up to 2048. The centre pixel is read back again at frame 120, once a
fullscreen window has its size.

Co-Authored-By: Claude Opus 5.5 <[email protected]>
Claude-Session: https://claude.ai/code/session_8b3490cccb4848b495dde1c5cdcacba0
This commit is contained in:
velzieandClaude Opus 5.5 committed 2026-10-24 20:50:48 -04:00
1 parent e76dc73110
commit 1f7965b4ba
1 file changed
+18 -6
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tests/games/src/sdl-fbo-blit.c
+18 -6
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@@ -2,13 +2,17 @@
* GL context, the scene drawn (fixed function) into a texture-rectangle
* framebuffer object, that blitted to the window's framebuffer, swap.
*
* sdl-fbo-blit [MODE] [FRAMES]
* sdl-fbo-blit [MODE] [FRAMES] [WINDOW]
*
* MODE: clear -- glClear of the window only (the floor)
* fbo -- clear + quad into the FBO, blit to 0 (Half-Life's path)
* info -- print GL_VERSION, GL_RENDERER and every extension, exit
* WINDOW: window (default), fullscreen (SDL_WINDOW_FULLSCREEN, as Half-Life
* opens by default) or desktop (SDL_WINDOW_FULLSCREEN_DESKTOP); a
* fullscreen window draws at its drawable size, read every frame.
* Prints "frame N" every 60 frames and reads back the window's centre pixel
* after the first frame ("centre r g b").
* after the first frame and the 121st ("centre r g b"), the second once a
* fullscreen window has its size.
*/
#include <SDL2/SDL.h>
#include <stdio.h>
@@ -59,9 +63,11 @@ int main(int argc, char **argv) {
setvbuf(stdout, 0, _IONBF, 0);
const char *mode = argc > 1 ? argv[1] : "fbo";
int frames = argc > 2 ? atoi(argv[2]) : 1 << 30;
const int w = 800, h = 600;
const char *how = argc > 3 ? argv[3] : "window";
Uint32 fs = !strcmp(how, "fullscreen") ? SDL_WINDOW_FULLSCREEN : !strcmp(how, "desktop") ? SDL_WINDOW_FULLSCREEN_DESKTOP : 0;
int w = 800, h = 600;
if (SDL_Init(SDL_INIT_VIDEO) != 0) { printf("SDL_Init: %s\n", SDL_GetError()); return 1; }
SDL_Window *win = SDL_CreateWindow("sdl-fbo-blit", 0, 0, w, h, SDL_WINDOW_OPENGL);
SDL_Window *win = SDL_CreateWindow("sdl-fbo-blit", 0, 0, w, h, SDL_WINDOW_OPENGL | fs);
if (!win) { printf("window: %s\n", SDL_GetError()); return 1; }
SDL_GLContext ctx = SDL_GL_CreateContext(win);
if (!ctx) { printf("context: %s\n", SDL_GetError()); return 1; }
@@ -94,7 +100,7 @@ int main(int argc, char **argv) {
if (!strcmp(mode, "fbo")) {
p_glGenTextures(1, &tex);
p_glBindTexture(GL_TEXTURE_RECTANGLE, tex);
p_glTexImage2D(GL_TEXTURE_RECTANGLE, 0, GL_RGBA8, w, h, 0, GL_RGBA, GL_UNSIGNED_BYTE, 0);
p_glTexImage2D(GL_TEXTURE_RECTANGLE, 0, GL_RGBA8, 2048, 2048, 0, GL_RGBA, GL_UNSIGNED_BYTE, 0);
p_glGenFramebuffers(1, &fbo);
p_glBindFramebuffer(GL_FRAMEBUFFER, fbo);
p_glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_RECTANGLE, tex, 0);
@@ -103,6 +109,12 @@ int main(int argc, char **argv) {
for (int f = 0; f < frames; f++) {
SDL_Event e;
while (SDL_PollEvent(&e)) if (e.type == SDL_QUIT) return 0;
if (fs) {
int dw = 0, dh = 0;
SDL_GL_GetDrawableSize(win, &dw, &dh);
if (dw != w || dh != h) printf("drawable %dx%d at frame %d\n", dw, dh, f);
if (dw > 0 && dh > 0 && dw <= 2048 && dh <= 2048) w = dw, h = dh;
}
p_glBindFramebuffer(GL_FRAMEBUFFER, fbo);
p_glViewport(0, 0, w, h);
p_glClearColor(0.1f, 0.2f, 0.6f, 1);
@@ -118,7 +130,7 @@ int main(int argc, char **argv) {
p_glBlitFramebuffer(0, 0, w, h, 0, 0, w, h, GL_COLOR_BUFFER_BIT, GL_LINEAR);
p_glBindFramebuffer(GL_FRAMEBUFFER, 0);
}
if (f == 0) {
if (f == 0 || f == 120) {
unsigned char px[4] = {0};
p_glReadPixels(w / 2, h / 2, 1, 1, GL_RGBA, GL_UNSIGNED_BYTE, px);
printf("centre %d %d %d error 0x%x\n", px[0], px[1], px[2], p_glGetError());