2D to 3D touch

gistfile1.txt

function setup()
    --settings for our rectangle (named "plane" below)
    plane={}
    plane.centre=vec3(0,0,0)
    plane.rotate=vec3(45,0,20)
    plane.size=vec2(500,500,0)
    
    --set up mesh, needed for shader
    plane.mesh=mesh()
    local s=plane.size
    local x1,y1,x2,y2,z=-s.x/2,-s.y/2,s.x/2,s.y/2,s.z
    plane.mesh.vertices={vec3(x1,y1,z),vec3(x2,y1,z),vec3(x2,y2,z),vec3(x2,y2,z),vec3(x1,y2,z),vec3(x1,y1,z)}
    plane.mesh.texCoords={vec2(0,0),vec2(1,0),vec2(1,1),vec2(1,1),vec2(0,1),vec2(0,0)}
    plane.mesh:setColors(color(255,255,0))
    
    parameter.text("Touch","") --shows results
    img=image(WIDTH,HEIGHT)
    shaderImg=image(WIDTH,HEIGHT)
    --CreateImageMap() --USE THIS if your plane/rectangle never changes position, otherwise delete    
end

--create an image map
function CreateImageMap()
    setContext(shaderImg)
    pushMatrix()
    SetupPerspective() --see comment below
    plane.mesh.shader=shader(PlaneShader.v,PlaneShader.f)
    plane.mesh:draw()
    setContext()
    popMatrix()
    plane.mesh.shader=nil
end

function draw()
    background(50)
    pushMatrix()
    --the camera position and rotations are put in a separate function, to ensure that 
    --when we draw the hidden shader image, we can get exactly the same settings
    SetupPerspective()
    --draw plane
    plane.mesh:draw()
    --draw touch to show it worked
    if p then 
        translate(p.x-plane.size.x/2,p.y-plane.size.y/2,1)
        fill(255,0,0)
        ellipse(0,0,20)
    end
    popMatrix()
end

--camera settings, also position and rotation of our rectangle/plane
function SetupPerspective()
    perspective()
    camera(0,0,900,0,0,-1)
    translate(plane.centre.x,plane.centre.y,plane.centre.z)
    rotate(plane.rotate.x,1,0,0)
    rotate(plane.rotate.y,0,1,0)
    rotate(plane.rotate.z,0,0,1)
end

function touched(t)
    if t.state==ENDED then
        p=GetPlaneTouchPoint(t)
        Touch=p
    end
end 

function GetPlaneTouchPoint(t)   
    --if your rectangle never changes position, delete these commented lines, you don't need them
    --however, if it moves around, you'll need to draw the shader image for each touch
    --in that case, uncomment all these lines
    --[[
    shaderImg=image(WIDTH,HEIGHT)
    setContext(shaderImg)
    pushMatrix()
    SetupPerspective()
    tx,ty=math.floor(t.x+0.5),math.floor(t.y+0.5)
    clip(tx-1,ty-1,3,3)
    plane.mesh.shader=shader(PlaneShader.v,PlaneShader.f)
    plane.mesh:draw()
    setContext()
    plane.mesh.shader=nil
    popMatrix()
    --]] 
    local x2,y2,x1y1=shaderImg:get(tx,ty)
    local y1=math.fmod(x1y1,16)
    local x1=(x1y1-y1)/16
    local x,y=(x1+x2*16)/4096*plane.size.x,(y1+y2*16)/4096*plane.size.y
    return vec2(x,y)
end

PlaneShader = {

v = [[
uniform mat4 modelViewProjection;
attribute vec4 position;
attribute vec2 texCoord;
varying highp vec2 vTexCoord;

void main()
{
    vTexCoord = texCoord;
    gl_Position = modelViewProjection * position;
}
]],
f = [[
precision highp float;
varying highp vec2 vTexCoord;

void main()
{
    highp vec2 T = vTexCoord * 4096.0;
    highp float x1=mod(T.x,16.0);
    highp float x2=(T.x - x1) / 16.0;
    highp float y1=mod(T.y,16.0);
    highp float y2=(T.y - y1) / 16.0;
    gl_FragColor = vec4(x2/255.0,y2/255.0,(x1*16.0+y1)/255.0,1.0);
}
]]}