MOAI radial progress shader.lua

local vsh = [=[
attribute vec4 position;
attribute vec2 uv;
attribute vec4 color;

varying MEDP vec4 colorVarying;
varying MEDP vec2 uvVarying;

void main () {
    gl_Position = position;
    uvVarying = uv;
    colorVarying = color;
}
]=]

local fsh = [=[
varying MEDP vec4 colorVarying;
varying MEDP vec2 uvVarying;

uniform float progress;
uniform float angleOffset;
uniform sampler2D sampler;

#define M_PI 3.141592653589793
#define M_2_PI 6.283185307179586

void main () {
    float a_rad = M_PI - atan(uvVarying[1] - 0.5, uvVarying[0] - 0.5);
    a_rad = a_rad / M_2_PI;
    a_rad = mod(angleOffset + a_rad, 1.0);

    // float a = step(progress, a_rad);
    // replace with proper step func
    %s

    LOWP vec4 color = texture2D ( sampler, uvVarying ) * a;
    gl_FragColor = color * colorVarying;
}
]=]

local normal = "float a = step(progress, a_rad);"
local inverse = "float a = step(a_rad, progress);"

local function CreateProgram(inv)
    program = MOAIShaderProgram.new()
    program:setVertexAttribute ( 1, 'position' )
    program:setVertexAttribute ( 2, 'uv' )
    program:setVertexAttribute ( 3, 'color' )

    local step = inv and inverse or normal
    local fragment = string.format(fsh, step)

    program:load(vsh, fragment)
    program:reserveUniforms(2)
    program:declareUniform(1, "progress", MOAIShaderProgram.UNIFORM_FLOAT)
    program:declareUniform(2, "angleOffset", MOAIShaderProgram.UNIFORM_FLOAT)

    return program
end

local function CircleProgressShader(inverse)
    local shader = MOAIShader.new()
    shader:setProgram(CreateProgram(inverse))
    shader:setAttr(1, 1)
    shader:setAttr(2, 0)
    
    return shader
end

local function floorTo(x, snap)
    return snap * math.floor(x / snap)
end

local function SetProgress(shader, p, steps)
    local p = 1 - p
    if steps then
        p = floorTo(p, 1 / steps)
    end
    shader:setAttr(1, p)
end

local function SetOffset(shader, o)
    shader:setAttr(2, o)
end


--=====================================================================--
-- Sample scene
--=====================================================================--

MOAISim.openWindow ( "test", 320, 480 )

viewport = MOAIViewport.new ()
viewport:setSize ( 320, 480 )
viewport:setScale ( 320, -480 )

layer = MOAILayer2D.new ()
layer:setViewport ( viewport )
MOAISim.pushRenderPass ( layer )

gfxQuad = MOAIGfxQuad2D.new ()
gfxQuad:setTexture ( "moai.png" )
gfxQuad:setRect ( -64, -64, 64, 64 )
gfxQuad:setUVRect ( 0, 0, 1, 1 )

prop = MOAIProp.new ()
prop:setDeck ( gfxQuad )
layer:insertProp ( prop )
    
shader = CircleProgressShader ()
prop:setShader ( shader )

thread = MOAICoroutine.new ()
thread:run ( function ()
    progress = 0
    while true do
        SetProgress ( shader, progress % 1 )
        progress = progress + 0.01
        coroutine.yield ()
    end
end )