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gradiente.htm
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gradiente.htm
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<!DOCTYPE HTML>
<html>
<head>
<script type="text/javascript">
var canvas;
var ctx;
//
// Ejemplo de Texture Mapping
//
// Tamaño del pixel
var dp = 1;
// Vamos a utilizar la transformcion
// T(x,y,z) = (x/z,y/z)
// Tambiene tenemos que ajustar el origen para quede aprox. en el centro de pantalla
// Para ello definimos:
var OX = 500;
var OY = 350;
// El aspect ratio es la relacion entre el ancho y el alto de la pantalla
var aspect = 1024.0/768.0;
function Transform_X(x,y,z)
{
// Perspectiva: Proyecto a Screen Space
var xs = x / z;
return xs;
}
function Transform_Y(x,y,z)
{
// Perspectiva: Proyecto a Screen Space
var ys = y / z;
return ys;
}
function Transform_Z(z)
{
return z;
}
// Dibuja un pixel
function DrawPixel(x,y,k)
{
x = OX + x*k;
y = OY - y*k;
ctx.beginPath();
ctx.moveTo(x,y);
ctx.lineTo(x+k,y);
ctx.lineTo(x+k,y+k);
ctx.lineTo(x,y+k);
ctx.lineTo(x,y);
ctx.closePath();
ctx.fill();
}
function min(x,y)
{
if(x <= y)
return x;
else
return y;
}
function max(x,y)
{
if(x >= y)
return x;
else
return y;
}
function barycentric_b( v1x, v1y , v2x , v2y ,v3x , v3y ,px,py)
{
var b,g;
var A = v1x - v3x;
var B = v2x - v3x;
var C = v3x - px;
var D = v1y - v3y;
var E = v2y - v3y;
var F = v3y - py;
var G = 0;
var H = 0;
var I = 0;
if(A==0 && B==0)
{
var temp = A;
A = D;
D = temp;
temp = B;
B = E;
E = temp;
temp = C;
C = F;
F = temp;
}
b = (B*(F+I) - C*(E+H)) / (A*(E+H) - B*(D+G));
//g = (A*(F+I) - C*(D+G)) / (B*(D+G) - A*(E+H));
return b;
}
function barycentric_g( v1x, v1y , v2x , v2y ,v3x , v3y ,px,py)
{
var b,g;
var A = v1x - v3x;
var B = v2x - v3x;
var C = v3x - px;
var D = v1y - v3y;
var E = v2y - v3y;
var F = v3y - py;
var G = 0;
var H = 0;
var I = 0;
if(A==0 && B==0)
{
var temp = A;
A = D;
D = temp;
temp = B;
B = E;
E = temp;
temp = C;
C = F;
F = temp;
}
//b = (B*(F+I) - C*(E+H)) / (A*(E+H) - B*(D+G));
g = (A*(F+I) - C*(D+G)) / (B*(D+G) - A*(E+H));
return g;
}
function tex2d(u, v)
{
u = (u*10) | 0;
v = (v*10) | 0;
if((u+v)%2==0)
return 'rgba(255,0,255,255)';
else
return 'rgba(0,0,0,255)';
}
// Proyecta y Dibuja un triangulo
function DrawTri( x0,y0,z0,r0,g0,b0,u0,v0,
x1,y1,z1,r1,g1,b1,u1,v1,
x2,y2,z2,r2,g2,b2,u2,v2)
{
// Primer punto
var X0 = Transform_X(x0,y0,z0);
var Y0 = Transform_Y(x0,y0,z0);
var Z0 = Transform_Z(z0);
// Segundo punto
var X1 = Transform_X(x1,y1,z1);
var Y1 = Transform_Y(x1,y1,z1);
var Z1 = Transform_Z(z1);
// Tercer punto
var X2 = Transform_X(x2,y2,z2);
var Y2 = Transform_Y(x2,y2,z2);
var Z2 = Transform_Z(z2);
// Calculo el bounding rect
var min_x = min(X0,min(X1,X2));
var min_y = min(Y0,min(Y1,Y2));
var max_x = max(X0,max(X1,X2));
var max_y = max(Y0,max(Y1,Y2));
// perspective correct interpolation
var pci = 1;
var rz0,rz1,rz2;
if(pci)
{
rz0 = 1/Z0;
rz1 = 1/Z1;
rz2 = 1/Z2;
u0 /= Z0;
v0 /= Z0;
u1 /= Z1;
v1 /= Z1;
u2 /= Z2;
v2 /= Z2;
}
for( i = min_y ; i<=max_y ; ++ i)
for( j = min_x ; j<=max_x ; ++ j)
{
// Determino si el punto esta adentro del triangulo
var b = barycentric_b(X0,Y0,X1,Y1,X2,Y2,j,i);
var g = barycentric_g(X0,Y0,X1,Y1,X2,Y2,j,i);
if((b >= 0) && (g >= 0) && (b +g <= 1))
{
var a = 1 - b - g;
var red = (r0*b + r1*g + r2*a ) | 0;
var green = (g0*b + g1*g + g2*a ) | 0;
var blue = (b0*b + b1*g + b2*a ) | 0;
var tu = u0*b + u1*g + u2*a;
var tv = v0*b + v1*g + v2*a;
// linear interpoloation (incorrect)
if(pci)
{
// hiperbolic interpoloation (perspective correct)
var rz = rz0*b + rz1*g + rz2*a;
tu /= rz;
tv /= rz;
}
//ctx.fillStyle = 'rgba(' + red.toString() + ',' + green.toString() + ',' + blue.toString() + ',255)';
//var U = tu*255 | 0
//var V = tv*255 | 0
//ctx.fillStyle = 'rgba(' + U.toString() + ',' + V.toString() + ',0,255)';
ctx.fillStyle = tex2d(tu,tv);
DrawPixel(j,i,dp);
}
}
}
function drawQuad()
{
var x0 = -320;
var y0 = -200;
var z0 = 1;
var u0 = 0;
var v0 = 0;
var r0 = 255;
var g0 = 0;
var b0 = 0;
var x1 = 320;
var y1 = -200;
var z1 = 1;
var u1 = 1;
var v1 = 0;
var r1 = 0;
var g1 = 255;
var b1 = 0;
var x2 = 320;
var y2 = 200;
var z2 = 5;
var u2 = 1;
var v2 = 1;
var r2 = 0;
var g2 = 0;
var b2 = 255;
var x3 = -320;
var y3 = 200;
var z3 = 5;
var u3 = 1;
var v3 = 0;
var r3 = 0;
var g3 = 0;
var b3 = 0;
DrawTri(x0,y0,z0,r0,g0,b0,u0,v0,
x1,y1,z1,r1,g1,b1,u1,v1,
x2,y2,z2,r2,g2,b2,u2,v2);
DrawTri(x0,y0,z0,r0,g0,b0,u0,v0,
x3,y3,z3,r3,g3,b3,u3,v3,
x2,y2,z2,r2,g2,b2,u2,v2);
}
function draw()
{
if (canvas.getContext)
{
ctx.fillStyle = 'rgba(240,240,240,255)';
ctx.fillRect(0,0,1000,800);
drawQuad(0);
}
}
function animate()
{
canvas = document.getElementById('mycanvas');
ctx = canvas.getContext('2d');
setInterval(draw, 100);
}
</script>
</head>
<body onload="animate();">
<canvas id="mycanvas" width="1000" height="700"></canvas>
</body>
</html>