Chroma Keying

--# Main
-- Chroma Keying

function setup()
    displayMode(OVERLAY)
    parameter.color("bg", color(0))
    parameter.boolean("cameraFront", false, function(cam)
        if cam then
            cameraSource(CAMERA_FRONT)
        else
            cameraSource(CAMERA_BACK)
        end
    end)
    parameter.number("minDistance", 0, 3, 0)
    parameter.number("maxDistance", 0, 3, 0.25)
    prevMin = minDistance
    prevMax = maxDistance
    m = mesh()
    rIdx = m:addRect(WIDTH / 2, HEIGHT / 2, WIDTH, HEIGHT)
    m.texture = CAMERA
    m.shader = shader(Shaders.ChromaKey.vS, Shaders.ChromaKey.fS)
    m.shader.minDistance = minDistance
    m.shader.maxDistance = maxDistance
    m.shader.key = color(0)
end

function draw()
    background(bg)
    if minDistance ~= prevMin then
        m.shader.minDistance = minDistance
        prevMin = minDistance
    end
    if maxDistance ~= prevMax then
        m.shader.maxDistance = maxDistance
        prevMax = maxDistance
    end
    m:draw()
end

function touched(touch)
    if touch.state == BEGAN then
        img = image(CAMERA)
        local x, y = math.floor(touch.x / WIDTH * img.width + 0.5), math.floor(touch.y / HEIGHT * img.height + 0.5)
        local r, g, b = img:get(x, y)
        m.shader.key = color(r, g, b)
    end
end

--# Shaders
Shaders = {
--shaderstart:ChromaKey
ChromaKey = {
vS = [[
//
// 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;
}
]],
fS = [[
//
// A basic fragment shader
//

//Default precision qualifier
precision highp float;

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

uniform vec4 key;

uniform float minDistance;

uniform float maxDistance;

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

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

void main()
{
    lowp vec4 col = texture2D(texture, vTexCoord);

    vec4 delta = col - key;
    float distance2 = dot(delta, delta);
    float weight = clamp((distance2 - minDistance) / (maxDistance - minDistance), 0.0, 1.0);

    //Set the output color to the texture color
    gl_FragColor = col * weight * vColor;
}
]],
},
--shaderend:ChromaKey
}