Route paint texture unit binding through GL backend

src/renderer_gl/opengl_capabilities.cpp

@@ -503,6 +503,18 @@ pp::foundation::Status clear_opengl_color_buffer_with_write_mask(
     return pp::foundation::Status::success();
 }
 
+pp::foundation::Status activate_opengl_texture_unit(
+    std::uint32_t unit_index,
+    OpenGlActiveTextureDispatch dispatch) noexcept
+{
+    if (dispatch.active_texture == nullptr) {
+        return pp::foundation::Status::invalid_argument("OpenGL active texture dispatch callback must not be null");
+    }
+
+    dispatch.active_texture(active_texture_unit(unit_index));
+    return pp::foundation::Status::success();
+}
+
 pp::foundation::Status apply_opengl_viewport(
     OpenGlViewportRect viewport,
     OpenGlViewportDispatch dispatch) noexcept

src/renderer_gl/opengl_capabilities.h

@@ -563,6 +563,10 @@ struct OpenGlClearDispatch {
     OpenGlClearFn clear = nullptr;
 };
 
+struct OpenGlActiveTextureDispatch {
+    OpenGlActiveTextureFn active_texture = nullptr;
+};
+
 struct OpenGlColorMaskedClearDispatch {
     OpenGlGetBooleanFn get_boolean = nullptr;
     OpenGlColorMaskFn color_mask = nullptr;
@@ -878,6 +882,9 @@ struct OpenGlMeshDeleteDispatch {
 [[nodiscard]] pp::foundation::Status clear_opengl_color_buffer_with_write_mask(
     OpenGlColorMaskedClear clear,
     OpenGlColorMaskedClearDispatch dispatch) noexcept;
+[[nodiscard]] pp::foundation::Status activate_opengl_texture_unit(
+    std::uint32_t unit_index,
+    OpenGlActiveTextureDispatch dispatch) noexcept;
 [[nodiscard]] pp::foundation::Status apply_opengl_viewport(
     OpenGlViewportRect viewport,
     OpenGlViewportDispatch dispatch) noexcept;