Fix bug #1270

Added an argument to the shader in order to flip the texture

examples/models/resources/shaders/glsl100/skybox.fs

@@ -4,23 +4,35 @@
 *
 *   Copyright (c) 2017 Victor Fisac
 *
+*	19-Jun-2020 - modified by Giuseppe Mastrangelo (@peppemas) - VFlip Support
+*
 **********************************************************************************************/
 
-#version 330
+#version 110
 
 // Input vertex attributes (from vertex shader)
 in vec3 fragPosition;
 
 // Input uniform values
 uniform samplerCube environmentMap;
+uniform bool vflipped;
 
 // Output fragment color
 out vec4 finalColor;
 
+vec4 flipTextureCube(samplerCube sampler, vec3 texCoord) {
+	return texture(sampler, vec3(texCoord.x,-texCoord.y,texCoord.z));
+}
+
 void main()
 {
     // Fetch color from texture map
-    vec3 color = texture(environmentMap, fragPosition).rgb;
+    vec3 color;
+
+    if (vflipped )
+    	color = flipTextureCube(environmentMap, fragPosition).rgb;
+    else 
+    	color = texture(environmentMap, fragPosition).rgb;
 
     // Apply gamma correction
     color = color/(color + vec3(1.0));