WebGL編程指南案例解析之繪制三角形
阿新 • • 發佈:2019-04-09
案例 for webgl new buffer sha its 參數 urn
//案例3.繪制三角形,將頂點數據存到緩沖區對象(gl.ARRAY_BUFFER)中,然後頂點著色器從裏面讀數據(3個頂點) //頂點著色器中去掉gl_PointSize = 10.0,繪制三角不能設置頂點的大小 //gl.drawArrays(gl.TRIANGLES,0,n);第一個參數改為三角,因為此時不是繪制點了 var vShader = ` attribute vec4 a_Position; void main(){ gl_Position = a_Position; } `; var fShader = ` void main(){ gl_FragColor= vec4(1.0, 0.0, 0.0, 1.0); } `; function main(){ //獲取canvas元素 var canvas = document.getElementById(‘webgl‘); //獲取webgl上下文 var gl = getWebGLContext(canvas); if(!gl){ console.log(‘Failed to get the rendering context for WebGL!‘); return; } //初始化著色器 if(!initShaders(gl,vShader,fShader)){ 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; } //用指定顏色填充webgl容器,就是設置背景 gl.clearColor(0.4, 0.5, 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;//點的個數 //創建緩沖區對象 var vertexBuffer = gl.createBuffer(); if(!vertexBuffer){ console.log(‘Failed to create the buffer object!‘); return -1; } //將緩沖區對象綁定到目標ARRAY_BUFFER gl.bindBuffer(gl.ARRAY_BUFFER,vertexBuffer); //往ARRAY_BUFFER gl.bufferData(gl.ARRAY_BUFFER,vertices,gl.STATIC_DRAW); //獲取shaderProgram中attribute變量‘a_Position’的地址 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; } //將緩沖區對象分配給a_Position變量 gl.vertexAttribPointer(a_Position,2,gl.FLOAT,false,0,0); //開啟著色器對緩沖區數據的訪問 gl.enableVertexAttribArray(a_Position); return n; } } main();
其實,繪制三角形和之前的繪制三個點的代碼很相似,只是:
在頂點著色器裏面,我們不能設置點的size了(gl_PointSize);
繪圖函數將從gl.drawArrays(gl.POINTS,0,n)變成gl.drawArrays(gl.TRIANGLES,0,n);
效果如下:
WebGL編程指南案例解析之繪制三角形