vo_gpu: attempt re-using the FBO format for p->output_tex

This allows RAs with support for non-opaque FBO formats to use a more
appropriate FBO format for the output tex, possibly enabling a more
efficient blit operation.

This requires distinguishing between real formats (which can be used to
create textures) and fake formats (e.g. ra_gl's FBO hack).

video/out/gpu/ra.h

@@ -85,6 +85,8 @@ struct ra_format {
                             // only applies to 2-component textures
     bool linear_filter;     // linear filtering available from shader
     bool renderable;        // can be used for render targets
+    bool dummy_format;      // is not a real ra_format but a fake one (e.g. FBO).
+                            // dummy formats cannot be used to create textures
 
     // If not 0, the format represents some sort of packed fringe format, whose
     // shader representation is given by the special_imgfmt_desc pointer.

video/out/gpu/video.c

@@ -3058,9 +3058,15 @@ void gl_video_render_frame(struct gl_video *p, struct vo_frame *frame,
                 if (frame->num_vsyncs > 1 && frame->display_synced &&
                     !p->dumb_mode && (p->ra->caps & RA_CAP_BLIT))
                 {
+                    // Attempt to use the same format as the destination FBO
+                    // if possible. Some RAs use a wrapped dummy format here,
+                    // so fall back to the fbo_format in that case.
+                    const struct ra_format *fmt = fbo.tex->params.format;
+                    if (fmt->dummy_format)
+                        fmt = p->fbo_format;
                     bool r = ra_tex_resize(p->ra, p->log, &p->output_tex,
                                            fbo.tex->params.w, fbo.tex->params.h,
-                                           p->fbo_format);
+                                           fmt);
                     if (r) {
                         dest_fbo = (struct ra_fbo) { p->output_tex };
                         p->output_tex_valid = true;

video/out/opengl/ra_gl.c

@@ -283,6 +283,8 @@ static struct ra_tex *gl_tex_create(struct ra *ra,
                                     const struct ra_tex_params *params)
 {
     GL *gl = ra_gl_get(ra);
+    assert(!params->format->dummy_format);
+
     struct ra_tex *tex = gl_tex_create_blank(ra, params);
     if (!tex)
         return NULL;
@@ -382,6 +384,7 @@ static const struct ra_format fbo_dummy_format = {
         .flags = F_CR,
     },
     .renderable = true,
+    .dummy_format = true,
 };
 
 // Create a ra_tex that merely wraps an existing framebuffer. gl_fbo can be 0

video/out/vulkan/ra_vk.c

@@ -511,6 +511,7 @@ static struct ra_tex *vk_tex_create(struct ra *ra,
                                     const struct ra_tex_params *params)
 {
     struct mpvk_ctx *vk = ra_vk_get(ra);
+    assert(!params->format->dummy_format);
 
     struct ra_tex *tex = talloc_zero(NULL, struct ra_tex);
     tex->params = *params;