vo_opengl: make blitting an explicit capability

Instead of merging it into render_dst. This is better for vulkan,
because blitting in vulkan both does not require a FBO *and* requires a
different image layout.

Also less "hacky" for OpenGL, since now the weird blit=FBO requirement
is an implementation detail of ra_gl

video/out/opengl/ra.h

@@ -90,7 +90,8 @@ struct ra_tex_params {
     const struct ra_format *format;
     bool render_src;        // must be useable as source texture in a shader
     bool render_dst;        // must be useable as target texture in a shader
-                            // this requires creation of a FBO
+    bool blit_src;          // must be usable as a blit source
+    bool blit_dst;          // must be usable as a blit destination
     // When used as render source texture.
     bool src_linear;        // if false, use nearest sampling (whether this can
                             // be true depends on ra_format.linear_filter)
@@ -359,8 +360,7 @@ struct ra_fns {
     // preserved. The formats of the textures must be losely compatible. The
     // dst texture can be a swapchain framebuffer, but src can not. Only 2D
     // textures are supported.
-    // Both textures must have tex->params.render_dst==true (even src, which is
-    // an odd GL requirement).
+    // The textures must have blit_src and blit_dst set, respectively.
     // Rectangles with negative width/height lead to flipping, different src/dst
     // sizes lead to point scaling. Coordinates are always in pixels.
     // Optional. Only available if RA_CAP_BLIT is set (if it's not set, it must

video/out/opengl/ra_gl.c

@@ -308,7 +308,8 @@ static struct ra_tex *gl_tex_create(struct ra *ra,
 
     gl_check_error(gl, ra->log, "after creating texture");
 
-    if (tex->params.render_dst) {
+    // Even blitting needs an FBO in OpenGL for strange reasons
+    if (tex->params.render_dst || tex->params.blit_src || tex->params.blit_dst) {
         if (!tex->params.format->renderable) {
             MP_ERR(ra, "Trying to create renderable texture with unsupported "
                    "format.\n");
@@ -378,6 +379,8 @@ struct ra_tex *ra_create_wrapped_fb(struct ra *ra, GLuint gl_fbo, int w, int h)
             .w = w, .h = h, .d = 1,
             .format = &fbo_dummy_format,
             .render_dst = true,
+            .blit_src = true,
+            .blit_dst = true,
         },
     };
 
@@ -598,8 +601,8 @@ static void gl_blit(struct ra *ra, struct ra_tex *dst, struct ra_tex *src,
 {
     GL *gl = ra_gl_get(ra);
 
-    assert(dst->params.render_dst);
-    assert(src->params.render_dst); // even src must have a FBO
+    assert(src->params.blit_src);
+    assert(dst->params.blit_dst);
 
     struct ra_tex_gl *src_gl = src->priv;
     struct ra_tex_gl *dst_gl = dst->priv;

video/out/opengl/utils.c

@@ -89,6 +89,7 @@ bool fbotex_change(struct fbotex *fbo, struct ra *ra, struct mp_log *log,
         .src_linear = true,
         .render_src = true,
         .render_dst = true,
+        .blit_src = true,
     };
 
     fbo->tex = ra_tex_create(fbo->ra, &params);