Route framebuffer texture copies through GL backend

src/util.h

@@ -201,6 +201,14 @@ std::string str_replace(const std::string& string, const std::string& search, co
 size_t curl_data_handler(void *contents, size_t size, size_t nmemb, void *userp);
 size_t curl_data_write(void *ptr, size_t size, size_t nmemb, FILE *stream);
 void check_OpenGLError(const char* stmt, const char* fname, int line);
+bool copy_framebuffer_to_texture_2d(
+    int destination_x,
+    int destination_y,
+    int source_x,
+    int source_y,
+    int width,
+    int height,
+    int level = 0) noexcept;
 inline glm::vec2 xy(const glm::vec4& v) { return glm::vec2(v.x, v.y); }
 inline glm::vec3 xyz(const glm::vec4& v) { return glm::vec3(v.x, v.y, v.z); }
 inline glm::vec2 zw(const glm::vec4& v) { return glm::vec2(v.z, v.w); }