Merge pull request #317 from olliwang/coordinate

Fixes a bug when applying `NVG_IMAGE_FLIPY`.

src/nanovg_gl.h

@@ -895,10 +895,14 @@ static int glnvg__convertPaint(GLNVGcontext* gl, GLNVGfragUniforms* frag, NVGpai
 		tex = glnvg__findTexture(gl, paint->image);
 		if (tex == NULL) return 0;
 		if ((tex->flags & NVG_IMAGE_FLIPY) != 0) {
-			float flipped[6];
-			nvgTransformScale(flipped, 1.0f, -1.0f);
-			nvgTransformMultiply(flipped, paint->xform);
-			nvgTransformInverse(invxform, flipped);
+			float m1[6], m2[6];
+			nvgTransformTranslate(m1, 0.0f, frag->extent[1] * 0.5f);
+			nvgTransformMultiply(m1, paint->xform);
+			nvgTransformScale(m2, 1.0f, -1.0f);
+			nvgTransformMultiply(m2, m1);
+			nvgTransformTranslate(m1, 0.0f, -frag->extent[1] * 0.5f);
+			nvgTransformMultiply(m1, m2);
+			nvgTransformInverse(invxform, m1);
 		} else {
 			nvgTransformInverse(invxform, paint->xform);
 		}