contributed simple shader example (#973)

Contributed simple shader example

examples/shaders/resources/shaders/glsl330/mask.fs

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+#version 330
+
+// Input vertex attributes (from vertex shader)
+in vec2 fragTexCoord;
+
+// Input uniform values
+uniform sampler2D texture0;
+uniform sampler2D mask;
+uniform int frame;
+
+// Output fragment color
+out vec4 finalColor;
+
+void main()
+{
+    vec4 maskColour = texture(mask, fragTexCoord+vec2(sin(-frame/150.0)/10.0,cos(-frame/170.0)/10.0));
+    if (maskColour.r < 0.25) discard;
+    vec4 texelColor = texture(texture0, fragTexCoord+vec2(sin(frame/90.0)/8.0,cos(frame/60.0)/8.0));
+
+    finalColor = texelColor * maskColour;
+}

examples/shaders/resources/shaders/glsl330/mask.vs

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+#version 330
+
+// Input vertex attributes
+in vec3 vertexPosition;
+in vec2 vertexTexCoord;
+
+// Input uniform values
+uniform mat4 mvp;
+uniform mat4 matModel;
+
+// Output vertex attributes (to fragment shader)
+out vec2 fragTexCoord;
+
+void main()
+{
+    // Send vertex attributes to fragment shader
+    fragTexCoord = vertexTexCoord;
+
+    // Calculate final vertex position
+    gl_Position = mvp*vec4(vertexPosition, 1.0);
+}