shader code

I’m not sure how to add an x and y offsets to the mask code. Could someone please help me…

uniform sampler2D imageTex;
uniform sampler2D maskTex;
void main (void) {
vec4 c1 = texture2D(imageTex, gl_TexCoord[0].st);
vec4 c2 = texture2D(maskTex, gl_TexCoord[0].st);
gl_FragColor = c1 * c2;

What x and y offsets? Define them.

Do not tell what they are but simply define them in your shader code.