Begin refactoring for non-NV12 support in EGLRenderer

app/shaders/egl_nv12.frag

@@ -0,0 +1,21 @@
+#version 300 es
+#extension GL_OES_EGL_image_external : require
+precision mediump float;
+out vec4 FragColor;
+
+in vec2 vTextCoord;
+
+uniform mat3 yuvmat;
+uniform vec3 offset;
+uniform samplerExternalOES plane1;
+uniform samplerExternalOES plane2;
+
+void main() {
+	vec3 YCbCr = vec3(
+		texture2D(plane1, vTextCoord)[0],
+		texture2D(plane2, vTextCoord).xy
+	);
+
+	YCbCr -= offset;
+	FragColor = vec4(clamp(yuvmat * YCbCr, 0.0, 1.0), 1.0f);
+}