vrend: Keep track of GL_FRAMEBUFFER_SRGB state and restore it after blits

When doing a blit in blit_int we use the same context that we use for drawing.
Now with qemu or crostini blits may be issued that are not issued by the guest
program so that it expects a GL_FRAMEBUFFER_SRGB state that might actually have
been clobbered.

Keep track of how GL_FRAMEBUFFER_SRGB is set when the framebuffer state is issued,
and restore its value after doing a blit via glBlitFramebuffer.

Thanks to Lepton Wu for tracking this down.

Fixes #126

Signed-off-by: Gert Wollny <gert.wollny@collabora.com>
Reviewed-by: Lepton Wu <lepton@chromium.org>

src/vrend_renderer.c

@@ -583,6 +583,7 @@ struct vrend_sub_context {
    bool depth_test_enabled;
    bool alpha_test_enabled;
    bool stencil_test_enabled;
+   bool framebuffer_srgb_enabled;
 
    GLuint program_id;
    int last_shader_idx;
@@ -2273,6 +2274,7 @@ static void vrend_hw_emit_framebuffer_state(struct vrend_context *ctx)
       glReadBuffer(GL_NONE);
       if (has_feature(feat_srgb_write_control)) {
          glDisable(GL_FRAMEBUFFER_SRGB_EXT);
+         ctx->sub->framebuffer_srgb_enabled = false;
       }
    } else if (has_feature(feat_srgb_write_control)) {
       struct vrend_surface *surf = NULL;
@@ -2291,6 +2293,7 @@ static void vrend_hw_emit_framebuffer_state(struct vrend_context *ctx)
       } else {
          glDisable(GL_FRAMEBUFFER_SRGB_EXT);
       }
+      ctx->sub->framebuffer_srgb_enabled = use_srgb;
    }
 
    if (vrend_state.use_gles &&
@@ -8279,6 +8282,13 @@ static void vrend_renderer_blit_int(struct vrend_context *ctx,
 
    glBindFramebuffer(GL_FRAMEBUFFER, ctx->sub->fb_id);
 
+   if (has_feature(feat_srgb_write_control)) {
+      if (ctx->sub->framebuffer_srgb_enabled)
+         glEnable(GL_FRAMEBUFFER_SRGB);
+      else
+         glDisable(GL_FRAMEBUFFER_SRGB);
+   }
+
    if (make_intermediate_copy) {
       vrend_renderer_resource_destroy(intermediate_copy);
       glDeleteFramebuffers(1, &intermediate_fbo);