wimmel_gl: Use GL_BGRA_EXT in readpixels

That is the native format graphics cards use, so we reach a fastpath for
the copy, which saves around 1s.

2 files changed, 21 insertions, 5 deletions

diff --git a/wimmel.frag b/wimmel.frag
index 22adcf9..58d633e 100644
--- a/wimmel.frag
+++ b/wimmel.frag
@@ -22,7 +22,7 @@ main()
 		}
 	}
 
-	gl_FragColor = vec4(float(diff < barrier), 0.0, 0.0, 1.0);
+	gl_FragColor = vec4(0.0, 0.0, float(diff < barrier), 1.0);
 }
 
 // vim:ft=c:
diff --git a/wimmel_gl.c b/wimmel_gl.c
index 0f271af..64fdda3 100644
--- a/wimmel_gl.c
+++ b/wimmel_gl.c
@@ -1,4 +1,6 @@
+#include <stdio.h>
 #include <stdlib.h>
+#include <string.h>
 #include <glib.h>
 #include <gdk-pixbuf/gdk-pixbuf.h>
 
@@ -8,6 +10,7 @@
 
 #include <EGL/egl.h>
 #include <GLES2/gl2.h>
+#include <GLES2/gl2ext.h>
 
 #else
 
@@ -355,16 +358,29 @@ main(int argc, char **argv)
 	draw();
 
 	glPixelStorei(GL_PACK_ALIGNMENT, 1);
-	stride = width * 4;
+	stride = width * sizeof(GLushort);
 	buffer = malloc(stride * height);
+
+#ifndef GLUT
+	if (!strstr((char *) glGetString(GL_EXTENSIONS),
+		    "GL_EXT_read_format_bgra")) {
+		fprintf(stderr, "GL_EXT_read_format_bgra not available\n");
+		exit(EXIT_FAILURE);
+	}
+#endif
 	glReadPixels(0, 0, width, height,
-		     GL_RGBA, GL_UNSIGNED_BYTE,
+		     GL_BGRA_EXT,
+#ifdef GL_EXT_read_format_bgra
+		     GL_UNSIGNED_SHORT_4_4_4_4_REV_EXT,
+#else
+		     GL_UNSIGNED_SHORT_4_4_4_4_REV,
+#endif
 		     buffer);
 
 	for (int j = 0; j < height; ++j) {
-		guchar *row = buffer + (height - 1 - j) * stride;
+		GLushort *row = (GLushort *) (buffer + (height - 1 - j) * stride);
 		for (int i = 0; i < width; ++i) {
-			if (*(row + i*4)) {
+			if (row[i] & 0x0f) {
 				color_t color = COLOR(255, 0, 0, 0);
 				for (int k = i; k < i+mwidth; k++) {
 					put_pixel(pixbuf, POINT(k, j), color);