Adding the shader examples

java/examples/Topics/Shaders/ImageMask/data/mask.glsl

@@ -0,0 +1,12 @@
+uniform sampler2D textureSampler;
+uniform sampler2D maskSampler;
+
+uniform vec2 texcoordOffset;
+varying vec4 vertColor;
+varying vec4 vertTexcoord;
+
+void main() {
+  vec4 texColor = texture2D(textureSampler, vertTexcoord.st).rgba;
+  vec4 maskColor = texture2D(maskSampler, vec2(vertTexcoord.s, 1.0 - vertTexcoord.t)).rgba;
+  gl_FragColor = mix(texColor, vec4(0, 0, 0, 0), 1.0 - maskColor.r);  
+}