diff --git a/Sources/viewport_server.cpp b/Sources/viewport_server.cpp
index 085b38b..fd3a0d3 100644
--- a/Sources/viewport_server.cpp
+++ b/Sources/viewport_server.cpp
@@ -461,19 +461,23 @@ void viewport_server_end_frame(void) {
         
         g_stagingWriteIdx = writeIdx ^ 1;
     }
-//#elif defined(KINC_OPENGL)
-//    glReadPixels(0, 0, g_viewport_state.width, g_viewport_state.height, GL_RGBA, GL_UNSIGNED_BYTE, pixels);
-//    size_t row_size = g_viewport_state.width * 4;
-//    for (int y = 0; y < g_viewport_state.height / 2; ++y) {
-//        uint8_t* row_top = pixels + y * row_size;
-//        uint8_t* row_bottom = pixels + (g_viewport_state.height - 1 - y) * row_size;
-//        for (size_t x = 0; x < row_size; ++x) {
-//            uint8_t temp = row_top[x];
-//            row_top[x] = row_bottom[x];
-//            row_bottom[x] = temp;
-//        }
-//    }
-//    memcpy(pixel_dest, pixels, pixel_size);
+#elif defined(KINC_OPENGL)
+    glReadBuffer(GL_BACK);
+    glReadPixels(0, 0, g_viewport_state.width, g_viewport_state.height,
+                 GL_RGBA, GL_UNSIGNED_BYTE, pixels);
+    // OpenGL reads bottom-to-top; flip to top-to-bottom to match D3D11 convention
+    size_t row_size = (size_t)g_viewport_state.width * 4;
+    for (int y = 0; y < g_viewport_state.height / 2; ++y) {
+        uint8_t* row_top = pixels + y * row_size;
+        uint8_t* row_bottom = pixels + (g_viewport_state.height - 1 - y) * row_size;
+        for (size_t x = 0; x < row_size; ++x) {
+            uint8_t temp = row_top[x];
+            row_top[x] = row_bottom[x];
+            row_bottom[x] = temp;
+        }
+    }
+    memcpy(pixel_dest, pixels, pixel_size);
+    pixels_written = true;
 #else
     // other platforms use render target
     if (g_viewport_state.render_target) {