Some basic shadow maps.

ShadowMap.lua

--# Main
-- ShadowMap

displayMode(FULLSCREEN)

function setup()
    scene = {main = {}, depth = {}}
    
    boxA, boxAdepth = box(0, -4, 0, 8)
    boxA.texture = readImage("Cargo Bot:Crate Yellow 2")
    boxA:setColors(color(255, 255))
    table.insert(scene.main, boxA)
    table.insert(scene.depth, boxAdepth)
    
    local numBoxes = 10 -- The number of boxes to fly around the scene
    
    for i = 1, numBoxes do
        math.randomseed(i)
        boxB, boxBdepth = box(0, 0, 0, 1)--box(math.random(-5, 5), math.random(0, 5), math.random(-5, 5), 0.5)
        boxB.texture = readImage("Cargo Bot:Crate Red 2")
        boxB:setColors(color(255, 255))
        table.insert(scene.main, boxB)
        table.insert(scene.depth, boxBdepth)
    end
    
    local s = 1024 -- The size of the shadowmap (512, 1024, or 2048 offer good FPS, but you can go up to 4096)
    
    depth = image(s / ContentScaleFactor, s / ContentScaleFactor)
    
    light = vec3(5, 5, 5)
    
    lightm = mesh() -- A cube to show where the light is
    lightm.vertices = Primitive:Cube(0.5, 0.5, 0.5, light.x, light.y, light.z)
    lightm:setColors(color(0))
    
    pos = vec3(0, 1, 0) -- Variables to handle camera movement and direction
    ang = vec2(0, 1)
    ang2 = vec2(1, -1):normalize()
    tpos = vec3(pos.x, pos.y, pos.z)
    tang = vec2(ang.x, ang.y)
    tang2 = vec2(ang2.x, ang2.y)
    
    mId = 0
    lId = 0
end

function move(k) -- Basic function to move and rotate the cubes to show off the shadowmaps
    if k > 1 then
        math.randomseed(k - 1)
        translate(math.random(-5, 5), math.random(0, 5), math.random(-5, 5))
        local dist = 4
        local rot = 360
        local speed = 0.25
        translate(noise(ElapsedTime * speed + k, 0, k * 16) * dist, noise(ElapsedTime * speed + k, 16, k * 16) * dist, noise(ElapsedTime * speed + k, 32, k * 16) * dist)
        rotate(noise(ElapsedTime * speed + k, 48, k * 16) * rot, 1, 0, 0)
        rotate(noise(ElapsedTime * speed + k, 64, k * 16) * rot, 0, 1, 0)
        rotate(noise(ElapsedTime * speed + k, 80, k * 16) * rot, 0, 0, 1)
    end
end

function draw()
    background(178, 211, 223, 255)
    
    local pmix = 0.0375 -- Smoothes the camera movement
    pos.x = pos.x * (1 - pmix) + tpos.x * pmix
    pos.y = pos.y * (1 - pmix) + tpos.y * pmix
    pos.z = pos.z * (1 - pmix) + tpos.z * pmix
    local amix = 0.1
    ang.x = ang.x * (1 - amix) + tang.x * amix
    ang.y = ang.y * (1 - amix) + tang.y * amix
    ang2.x = ang2.x * (1 - amix) + tang2.x * amix
    ang2.y = ang2.y * (1 - amix) + tang2.y * amix
    
    setContext(depth, true) -- Drawing into the depth map
    background(255, 255)
    camera(light.x, light.y, light.z, 0, 0, 0, 0, 1, 0)
    perspective(150, depth.width / depth.height, 0.001, 65536)
    
    local lightModelViewProjection = modelMatrix() * viewMatrix() * projectionMatrix()
    
    for k, v in ipairs(scene.depth) do
        pushMatrix()
        
        move(k)
        
        v.shader.lightPos = light
        v.shader.model = modelMatrix()
        v:draw()
        
        popMatrix()
    end
    
    setContext() -- Drawing onto the screen
    
    camera(pos.x, pos.y, pos.z, pos.x + ang.x * ang2.x, pos.y + ang2.y, pos.z + ang.y * ang2.x, 0, 1, 0)
    --camera(light.x, light.y, light.z, 0, 0, 0, 0, 1, 0) -- Uncomment to show the scene from the light's position
    perspective(80, WIDTH / HEIGHT, 0.001, 65536)
    
    lightm:draw() -- Comment out if you are looking at the scene from the light's position
    
    for k = #scene.main, 1, -1 do
        local v = scene.main[k]
        
        pushMatrix()
        
        move(k)
        
        v.shader.lightModelViewProjection = lightModelViewProjection
        v.shader.shadowMap = depth
        v.shader.lightPos = light
        v.shader.model = modelMatrix()
        v:draw()
        
        popMatrix()
    end
    
    ortho()
    viewMatrix(matrix())
    resetMatrix()
    
    tint(255, 127) -- Small preview of the light's perspective (depth map)
    sprite(depth, 100, 100, 200, 200)
    
    fill(255)
    font("HelveticaNeue-Light")
    fontSize(24)
    local w, h = textSize(FPS)
    text(FPS, w / 2, HEIGHT - h / 2)
    
    collectgarbage()
    collectgarbage()
    collectgarbage()
end

function touched(touch) -- Handles camera movement and direction
    if touch.state == BEGAN then
        if touch.x < WIDTH / 2 and mId == 0 then
            mId = touch.id
        elseif touch.x >= WIDTH / 2 and lId == 0 then
            lId = touch.id
        end
    end
    
    if touch.id == mId then
        local speed = 1 / 64
        tpos.x = tpos.x + tang:rotate(math.pi / 2).x * touch.deltaX * speed
        tpos.z = tpos.z + tang:rotate(math.pi / 2).y * touch.deltaX * speed
        tpos.x = tpos.x + tang.x * tang2.x * touch.deltaY * speed
        tpos.z = tpos.z + tang.y * tang2.x * touch.deltaY * speed
        tpos.y = tpos.y + tang2.y * touch.deltaY * speed
    elseif touch.id == lId then
        tang = tang:rotate(math.rad(touch.deltaX / 2))
        tang2 = tang2:rotate(math.rad(touch.deltaY / 2))
        if tang2.x < 0.01 then
            if tang2.y < 0 then
                tang2 = vec2(0.01, -1):normalize()
            else
                tang2 = vec2(0.01, 1):normalize()
            end
        end
    end
    
    if touch.state == ENDED then
        if touch.id == mId then
            mId = 0
        elseif touch.id == lId then
            lId = 0
        end
    end
end

function box(px, py, pz, pw, ph, pl)
    local x = px or 0
    local y = py or x
    local z = pz or x
    local w = pw or 1
    local h = ph or w
    local l = pl or w
    
    local main = mesh()
    main.vertices = Primitive:Cube(w, h, l, x, y, z)
    main.texCoords = Primitive:CubeTexCoords()
    main:setColors(color(255))
    main.shader = shader("Shadow")
    
    local depth = mesh()
    depth.vertices = Primitive:Cube(w, h, l, x, y, z)
    depth.texCoords = Primitive:CubeTexCoords()
    depth.shader = shader("Depth")
    
    return main, depth
end

-- Function tweak to make shaders easier, so I can call shader("Depth") instead of shader(Shaders.Depth.vS, Shaders.Depth.fS)
local _shader = shader
function shader(...)
    if select("#", ...) == 1 then
        local data = Shaders[select(1, ...)]
        if data ~= nil then
            return _shader(data.vS, data.fS)
        else
            return _shader(...)
        end
    else
        return _shader(...)
    end
end

--# Shaders
-- Shaders
-- "Depth" shader encodes the distance between a fragment and the light
-- "Shadow" shader takes the encoded distance and calculates shadows with it

Shaders = {
--shaderstart:Depth
Depth = {
vS = [[
//
// A basic vertex shader
//

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

uniform mat4 model;

//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;
varying vec4 vPosition;

void main()
{
    //Pass the mesh color to the fragment shader
    vColor = color;
    vTexCoord = texCoord;
    vPosition = model * position;
    
    //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 vec3 lightPos;

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

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

varying vec4 vPosition;

void main()
{
    highp float dist = distance(lightPos, vPosition.xyz);
    lowp vec4 col = vec4(mod(dist, 1.0), mod(floor(dist) / 50.0, 1.0), floor(dist / 50.0) / 50.0, 1.0);
    
    // Encoded RGB data:
    // full red = 1 unit
    // full green = 50 units
    // full blue = 2500 units
    // Add that all together and you get the encoded distance

    //Set the output color to the texture color
    gl_FragColor = col;
}
]],
},
--shaderend:Depth
--shaderstart:Shadow
Shadow = {
vS = [[
//
// A basic vertex shader
//

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

uniform mat4 model;

//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;
varying vec4 vPosition;

void main()
{
    //Pass the mesh color to the fragment shader
    vColor = color;
    vTexCoord = texCoord;
    vPosition = model * position;
    
    //Multiply the vertex position by our combined transform
    gl_Position = modelViewProjection * position;
}
]],
fS = [[
//
// A basic fragment shader
//

//Default precision qualifier
precision highp float;

uniform mat4 lightModelViewProjection;

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

uniform lowp sampler2D shadowMap;

uniform vec3 lightPos;

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

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

varying vec4 vPosition;

void main()
{
    if (!gl_FrontFacing) discard;
    
    //Sample the texture at the interpolated coordinate
    lowp vec4 col = texture2D( texture, vTexCoord );
    
    vec4 m = lightModelViewProjection * vPosition;
    vec2 lightTexCoord = vec2((m[0] / m[3] + 1.0) / 2.0, (m[1] / m[3] + 1.0) / 2.0); // The texture coordinate of this fragment from the light's perspective
    
    highp vec4 lightCol = texture2D(shadowMap, lightTexCoord.xy); // The encoded distance
    highp float lightDist = lightCol.r + lightCol.g * 50.0 + floor(lightCol.b * 2500.0); // The decoded distance between whatever fragment in this direction is closest to the light and the light itself
    highp float dist = distance(vPosition.xyz, lightPos); // Distance between this fragment and the light
        
    if (dist > lightDist + 0.2) col.rgb *= 0.5; // You can change the effect here to get different shadows
    
    //Set the output color to the texture color
    gl_FragColor = col * vColor;
}
]],
},
--shaderend:Shadow
}
--# Primitive
Primitive = class()
-- Primitive class originally by @spacemonkey
-- Edited by @SkyTheCoder to add options for width, height, length, and position, also to generate texture coordinates for the cube
 
--primitves gives basic mesh building for cubes and isospheres
--triangles are wound consistently to avoid gl_facing issues
 
function Primitive:Cube(w, h, l, x, y, z)
    local s = 1
    w = w or 1
    h = h or w
    l = l or h
    x = x or 0
    y = y or 0
    z = z or 0
    local vertices = {
      vec3(-0.5*s, -0.5*s,  0.5*s), -- Left  bottom front
      vec3( 0.5*s, -0.5*s,  0.5*s), -- Right bottom front
      vec3( 0.5*s,  0.5*s,  0.5*s), -- Right top    front
      vec3(-0.5*s,  0.5*s,  0.5*s), -- Left  top    front
      vec3(-0.5*s, -0.5*s, -0.5*s), -- Left  bottom back
      vec3( 0.5*s, -0.5*s, -0.5*s), -- Right bottom back
      vec3( 0.5*s,  0.5*s, -0.5*s), -- Right top    back
      vec3(-0.5*s,  0.5*s, -0.5*s), -- Left  top    back
    }
 
    -- now construct a cube out of the vertices above
    v = {
      -- Front
      vertices[1], vertices[2], vertices[3],
      vertices[1], vertices[3], vertices[4],
      -- Right
      vertices[2], vertices[6], vertices[7],
      vertices[2], vertices[7], vertices[3],
      -- Back
      vertices[6], vertices[5], vertices[8],
      vertices[6], vertices[8], vertices[7],
      -- Left
      vertices[5], vertices[1], vertices[4],
      vertices[5], vertices[4], vertices[8],
      -- Top
      vertices[4], vertices[3], vertices[7],
      vertices[4], vertices[7], vertices[8],
      -- Bottom
      vertices[5], vertices[6], vertices[2],
      vertices[5], vertices[2], vertices[1],
    }
    for i, j in ipairs(v) do
        v[i] = vec3(j.x * w + x, j.y * h + y, j.z * l + z)
    end
    return v
end

function Primitive:CubeTexCoords(w, h, x)
    w = w or 1
    h = h or w
    x = x or Primitive:Cube(1)
    local ret = {}
    for i = 1, #x / 3 do
        table.insert(ret, vec2(0.0, 0.0))
        table.insert(ret, vec2(w, 0.0))
        table.insert(ret, vec2(w, h))
        table.insert(ret, vec2(0.0, 0.0))
        table.insert(ret, vec2(w, h))
        table.insert(ret, vec2(0.0, h))
    end
    return ret
end
 

--# FPS
FPS = 0 -- Code to calculate accurate frames per secoond
local frames = 0
local time = 0
tween.delay(0.001, function()
    local d = draw
    draw = function()
        frames = frames + 1
        if math.floor(ElapsedTime) ~= math.floor(time) then
            FPS = frames - 1
            frames = 1
        end
        time = ElapsedTime
        d()
    end
end)