Grass Simulation in Codea

Grass Simulation.lua

--# Main
-- Grass

function setup()
    displayMode(FULLSCREEN)
    R,H = 40,1
    base = mesh()
    base.vertices = {
        vec3(-1,0,-1), vec3(1,0,-1),
        vec3(1,0,1), vec3(1,0,1),
        vec3(-1,0,1), vec3(-1,0,-1)      
    }
    base:setColors(
    color(27, 40, 30, 255))    
    g = Grass()
end


function draw()
    background(0, 0, 0, 255)
    camera(0,H,5,0,0,0)
    perspective(45)
    rotate(R, 0,1,0)
    g:draw()
    scale(4)
    base:draw()
end

function touched(touch)
    if touch.state == MOVING then
        R = R + touch.deltaX*.5
        H = math.max(H - touch.deltaY*.02, .5)
    end
end
--# Grass
Grass = class()

function mult(m, v)
    return vec3(
        m[1]*v.x+m[2]*v.y+m[3]*v.z,
        m[5]*v.x+m[6]*v.y+m[7]*v.z,
        m[9]*v.x+m[10]*v.y+m[11]*v.z
    )
end

function Grass:init(x)
    self.m = mesh()
--    http.request("https://dl.dropbox.com/s/2kboo35minb8opx/Photo%202013-03-19%2010%2011%2028.jpg?token_hash=AAFsT-JmLRpPP5F0pet5tZHo2c0-aaOu7LpwzHCWXVPS_g&dl=1",function(data)
 --       self.m.texture = data
 --   end)
    self.m.texture = readImage("Documents:Grasses")
    self.m.shader = GrassShader
    
    local sq = {
        vec3(0,0,0), vec3(1,0,0),
        vec3(1,1,0), vec3(1,1,0),
        vec3(0,1,0), vec3(0,0,0)      
    }
    local vs, uvs = {}, {}
    for x=-5,5 do for z=-5,5 do
        local r = vec3(math.random(-.5,.5), 0, math.random(-.5,.5))
        local h = math.random(1,1.3)
        for j = 0,2 do
            local m = matrix():rotate(60*j,0,1,0)
            for i,v in ipairs(sq) do
                local p = v - vec3(.5,0,0)
                p.y = p.y * h
                p = mult(m,p) + vec3(x,0,z)*.6 + r
                table.insert(vs, p)
                table.insert(uvs, v)
            end
        end
    end end
    self.m.vertices = vs
    self.m.texCoords = uvs
    self.m:setColors(255,255,255,255)
end

function Grass:draw()
    self.m.shader.time = ElapsedTime
    self.m:draw()
end


--# GrassShader
GrassShader = shader()
GrassShader.vertexProgram = [[
uniform mat4 modelViewProjection;
attribute vec4 position;
attribute vec4 color;
attribute vec2 texCoord;

varying lowp vec4 vColor;
varying highp vec2 vTexCoord;
uniform highp float time;

// Noise
float hash( float n ) {
    return fract(sin(n)*43758.5453);
}
float noise( in vec2 x ) {
    vec2 p = floor(x);
    vec2 f = fract(x);
    f = f*f*(3.0-2.0*f);
    float n = p.x + p.y*57.0;
    float res = mix(mix( hash(n+  0.0), hash(n+  1.0),f.x), mix( hash(n+ 57.0), hash(n+ 58.0),f.x),f.y);
    return res;
} 
float fbm( vec2 p ) {
        float f = 0.0;
        f += 0.50000*noise( p ); p = p*2.02;
   //     f += 0.25000*noise( p ); p = p*2.03;
    //    f += 0.12500*noise( p ); p = p*2.01;
        f += 0.06250*noise( p ); p = p*2.04;
        f += 0.03125*noise( p );
        return f/0.984375;
}

void main()
{
    vColor = color;
    vTexCoord = vec2(texCoord.x, texCoord.y);
    vec4 p =  modelViewProjection * position;
    if(vTexCoord.y > .9) {
        float n = fbm(p.xy*time*.2)*4. - 2.;
        p = p + vec4(n,0.,0.,0.);
    }
    lowp vec4 nor = normalize(p);

    lowp float vShade = (dot(nor.xyz,vec3(1.,0.,0.))+.4)/1.2;
    if (vShade >1.0) {vShade=1.0;}
    if (vShade <0.4) {vShade=0.4;}
    vColor.rgb = vColor.rgb * vShade;
    
    gl_Position = p;
}

]]
GrassShader.fragmentProgram = [[
uniform lowp sampler2D texture;
varying lowp vec4 vColor;
varying highp vec2 vTexCoord;

void main()
{
    lowp vec4 col = texture2D( texture, vTexCoord );
    if(col.r > .5) discard;
    gl_FragColor = col*vColor;
}
]]