Allow user to flipY in 'rtt' textures (#293)

Noticed this and wanted to fix it real quick

Author: frank-weindel

examples/tests/rtt-dimension.ts

@@ -185,6 +185,10 @@ export default async function test({ renderer, testRoot }: ExampleSettings) {
       width: 100,
       height: 100,
       texture: nestedRTTNode1.texture,
+      // Flip every other one of them
+      textureOptions: {
+        flipY: i % 2 === 1,
+      },
     });
   }
 

src/core/renderers/webgl/WebGlCoreRenderer.ts

@@ -282,9 +282,9 @@ export class WebGlCoreRenderer extends CoreRenderer {
     const flipX = textureOptions?.flipX ?? false;
     let flipY = textureOptions?.flipY ?? false;
 
-    // always flip Y for render textures
+    // always flip flipY for render textures
     if (texture instanceof RenderTexture) {
-      flipY = true;
+      flipY = !flipY;
     }
 
     let texCoordX1 = 0;