opengl: flip Y axis during framebuffer blit

src/apprt/gtk/class/render_surface.zig

@@ -158,15 +158,6 @@ pub const RenderSurface = extern struct {
         const h = widget.getHeight();
         if (w == 0 or h == 0) return;
 
-        // In OpenGL +Y is up but in GSK (and DirectX, Metal, Vulkan, etc.)
-        // +Y is down. We therefore might need to flip the rendered image.
-        snap.save();
-        defer snap.restore();
-        if (comptime !rendererpkg.Renderer.API.custom_shader_y_is_down) {
-            snap.translate(&.{ .f_x = 0, .f_y = @floatFromInt(h) });
-            snap.scale(1, -1);
-        }
-
         snap.appendTexture(texture, &.{
             .f_origin = .{ .f_x = 0, .f_y = 0 },
             .f_size = .{ .f_width = @floatFromInt(w), .f_height = @floatFromInt(h) },

src/renderer/opengl/Target.zig

@@ -165,15 +165,19 @@ pub fn exportDmabuf(
     const draw_bind = try self.export_framebuffer.bind(.draw);
     defer draw_bind.unbind();
 
+    // Flip the Y axis during the blit so apprts don't have to
+    // handle this. We do this explicitly in OpenGL only
+    // because it's the only one that thinks +Y should point up
+    // for some reason.
     try gl.blitFramebuffer(
         0,
         0,
         @intCast(self.width),
         @intCast(self.height),
         0,
-        0,
-        @intCast(self.width),
         @intCast(self.height),
+        @intCast(self.width),
+        0,
         .{ .color_buffer_bit = true },
         .nearest,
     );