gistfile1.txt

-- StencilMask

-- Use this function to perform your initial setup
function setup()
    parameter.boolean("Negative",false)
    img=readImage("Cargo Bot:Starry Background")
    stencilImg=readImage("Planet Cute:Character Princess Girl")
    m=mesh()
    u=m:addRect(0,0,img.width,img.height)
    m:setRectTex(u,0,0,1,1)
    m.texture=img
    m.shader = shader(stencilShader.vertexShader, stencilShader.fragmentShader)
    m.shader.texture2=stencilImg
    m.shader.negative=Negative
end

function draw()
    background(200)
    pushMatrix()
    translate(300,300)
    m.shader.negative=Negative
    m:draw()
    popMatrix()
end

stencilShader = {
vertexShader = [[
//
// A basic vertex shader
//

//This is the current model * view * projection matrix
// Codea sets it automatically
uniform mat4 modelViewProjection;

//This is the current mesh vertex position, color and tex coord
// Set automatically
attribute vec4 position;
attribute vec4 color;
attribute vec2 texCoord;

//This is an output variable that will be passed to the fragment shader
varying lowp vec4 vColor;
varying highp vec2 vTexCoord;

void main()
{
    //Pass the mesh color to the fragment shader
    vColor = color;
    vTexCoord = texCoord;

    //Multiply the vertex position by our combined transform
    gl_Position = modelViewProjection * position;
}

]],
fragmentShader = [[
//
// A basic fragment shader
//

//Default precision qualifier
precision highp float;

//This represents the current texture on the mesh
uniform lowp sampler2D texture;

uniform lowp sampler2D texture2;
uniform bool negative;

//The interpolated vertex color for this fragment
varying lowp vec4 vColor;

//The interpolated texture coordinate for this fragment
varying highp vec2 vTexCoord;

void main()
{
    //Sample the texture at the interpolated coordinate
    lowp vec4 col1 = texture2D( texture, vTexCoord );
    lowp vec4 col2 = texture2D( texture2, vTexCoord );
    if (negative)
        {if (col2.a>0.)  gl_FragColor = col1; else discard;} 
    else if (col2.a==0.) gl_FragColor = col1; else discard;
}

]]}