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var VSHADER_SOURCE = 'attribute vec4 a_Position;'+ 'void main(){'+ 'gl_Position=a_Position;'+ '}';
var FSHADER_SOURCE= 'void main(){'+ 'gl_FragColor = vec4(1.0, 0.0, 0.0, 1.0);'+ '}';
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; }
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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