Keep global state clean

Unbind the FBO+texture after initialization, bind it before
rendering, unbind it after, re-bind the texture to scrape the
data, unbind the texture.

Signed-off-by: David Oberhollenzer <goliath@infraroot.at>

shadermeh.c

@@ -232,10 +232,13 @@ int main(int argc, char **argv)
 		glBindTexture(GL_TEXTURE_2D, fbo_tex);
 		glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, width, height, 0,
 			     GL_RGBA, GL_UNSIGNED_BYTE, NULL);
+		glBindTexture(GL_TEXTURE_2D, 0);
 
 		glBindFramebuffer(GL_FRAMEBUFFER, fbo);
 		glFramebufferTexture(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0,
 				     fbo_tex, 0);
+
+		glBindFramebuffer(GL_FRAMEBUFFER, 0);
 	} else {
 		window_show(wnd);
 	}
@@ -244,6 +247,10 @@ int main(int argc, char **argv)
 	while (to_stdout || window_handle_events()) {
 		/* render image to FBO */
 		clock_gettime(CLOCK_MONOTONIC_RAW, &frame_start);
+
+		if (to_stdout)
+			glBindFramebuffer(GL_FRAMEBUFFER, fbo);
+
 		glClear(GL_COLOR_BUFFER_BIT);
 		glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);
 
@@ -255,9 +262,14 @@ int main(int argc, char **argv)
 
 		/* get image from FBO, dump to stdout */
 		if (to_stdout) {
+			glBindFramebuffer(GL_FRAMEBUFFER, 0);
+			glBindTexture(GL_TEXTURE_2D, fbo_tex);
+
 			glGetTexImage(GL_TEXTURE_2D, 0, GL_RGBA,
 				      GL_UNSIGNED_BYTE, fb32);
 
+			glBindTexture(GL_TEXTURE_2D, 0);
+
 			convert_for_ffmpeg(fb32, fb24, width, height);
 
 			if (write_retry(STDOUT_FILENO, fb24,