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var VSHADER_SOURCE = 'attribute vec4 a_Position;\n' + 'uniform float u_CosB, u_SinB;\n' + 'void main() {\n' + 'gl_Position.x = a_Position.x * u_CosB - a_Position.y * u_SinB;\n' + 'gl_Position.y = a_Position.x * u_SinB + a_Position.y * u_CosB;\n' + 'gl_Position.z = a_Position.z;\n' + 'gl_Position.w = 1.0;\n' + '}\n';
var FSHADER_SOURCE= 'void main(){'+ 'gl_FragColor = vec4(1.0, 0.0, 0.0, 1.0);'+ '}';
var ANGLE = 90.0;
function main(){
var canvas = document.getElementById("webgl"); if(!canvas){ console.log("Failed to retrieve the <canvas> element"); return; }
var gl = getWebGLContext(canvas); if(!gl){ console.log("Failed to get the rendering context for WebGL"); return; }
if(!initShaders(gl,VSHADER_SOURCE,FSHADER_SOURCE)){ console.log("Failed to initialize shaders."); return; }
var n = initVertexBuffers(gl); if (n < 0) { console.log('Failed to set the positions of the vertices'); return; }
var radian = Math.PI * ANGLE / 180.0; var cosB = Math.cos(radian); var sinB = Math.sin(radian);
var u_CosB = gl.getUniformLocation(gl.program, 'u_CosB'); if(u_CosB < 0){ console.log("Failed to get the storage location of u_CosB"); return; }
var u_SinB = gl.getUniformLocation(gl.program, 'u_SinB'); if(u_SinB < 0){ console.log("Failed to get the storage location of u_SinB"); return; } gl.uniform1f(u_CosB, cosB); gl.uniform1f(u_SinB, sinB);
gl.clearColor(0.0, 0.0, 0.0, 1.0);
gl.clear(gl.COLOR_BUFFER_BIT);
gl.drawArrays(gl.TRIANGLES, 0, n); }
function initVertexBuffers(gl) { var vertices = new Float32Array( [0.0, 0.5, -0.5, -0.5, 0.5, -0.5] ); var n=3;
var vertexBuffer = gl.createBuffer(); if(!vertexBuffer){ console.log("Failed to create thie buffer object"); return -1; }
gl.bindBuffer(gl.ARRAY_BUFFER, vertexBuffer);
gl.bufferData(gl.ARRAY_BUFFER, vertices, gl.STATIC_DRAW);
var a_Position = gl.getAttribLocation(gl.program, 'a_Position'); if(a_Position < 0){ console.log("Failed to get the storage location of a_Position"); return -1; }
gl.vertexAttribPointer(a_Position, 2, gl.FLOAT, false, 0, 0);
gl.enableVertexAttribArray(a_Position);
return n; }
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