webgl第35課-深度緩衝-正確處理影象的位置關係
阿新 • • 發佈：2018-12-19
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上一節課我們學習了 透視投影矩陣之不同位置的彩色三角形
這一節課我們將學習 正確處理影象的位置關係
如果沒有在上一節的基礎上把設定頂點位置和顏色的順序打亂，會出現下面這樣的情況：
顯然這種情況正常來說不是我們需要的，所以我們加入了深度緩衝！
本案例把繪製三角形的順序打亂了，執行效果如下：
<!DOCTYPE html> <html lang="en"> <head> <meta charset="utf-8" /> <title>webgl第35課-深度緩衝之正確處理影象的位置關係</title> </head> <body onload="main()"> <canvas id="webgl" width="400" height="400"> Please use a browser that supports "canvas" </canvas> <script src="../lib/webgl-utils.js"></script> <script src="../lib/webgl-debug.js"></script> <script src="../lib/cuon-utils.js"></script> <script src="../lib/cuon-matrix.js"></script> <script src="DepthBuffer.js"></script> </body> </html>
// DepthBuffer.js (c) 2012 matsuda // Vertex shader program var VSHADER_SOURCE = 'attribute vec4 a_Position;\n' + 'attribute vec4 a_Color;\n' + 'uniform mat4 u_mvpMatrix;\n' + 'varying vec4 v_Color;\n' + 'void main() {\n' + ' gl_Position = u_mvpMatrix * a_Position;\n' +//模型檢視投影矩陣*原始頂點座標 ' v_Color = a_Color;\n' + '}\n'; // Fragment shader program var FSHADER_SOURCE = '#ifdef GL_ES\n' + 'precision mediump float;\n' + '#endif\n' + 'varying vec4 v_Color;\n' + 'void main() {\n' + ' gl_FragColor = v_Color;\n' + '}\n'; function main() { // Retrieve <canvas> element var canvas = document.getElementById('webgl'); // Get the rendering context for WebGL var gl = getWebGLContext(canvas); if (!gl) { console.log('Failed to get the rendering context for WebGL'); return; } // Initialize shaders if (!initShaders(gl, VSHADER_SOURCE, FSHADER_SOURCE)) { console.log('Failed to intialize shaders.'); return; } // Set the vertex coordinates and color (the blue triangle is in the front) var n = initVertexBuffers(gl); if (n < 0) { console.log('Failed to set the vertex information'); return; } // Specify the color for clearing <canvas> gl.clearColor(0.0, 0.0, 0.0, 1.0); // 深度檢測（開啟隱藏面消除功能） gl.enable(gl.DEPTH_TEST); // Get the storage location of u_mvpMatrix var u_mvpMatrix = gl.getUniformLocation(gl.program, 'u_mvpMatrix'); if (!u_mvpMatrix) { console.log('Failed to get the storage location of u_mvpMatrix'); return; } var modelMatrix = new Matrix4(); // Model matrix var viewMatrix = new Matrix4(); // View matrix var projMatrix = new Matrix4(); // Projection matrix var mvpMatrix = new Matrix4(); // Model view projection matrix // Calculate the view matrix and the projection matrix modelMatrix.setTranslate(0.75, 0, 0); viewMatrix.setLookAt(0, 0, 5, 0, 0, -100, 0, 1, 0); projMatrix.setPerspective(30, canvas.width/canvas.height, 1, 100); // Calculate the model view projection matrix mvpMatrix.set(projMatrix).multiply(viewMatrix).multiply(modelMatrix); // Pass the model view projection matrix gl.uniformMatrix4fv(u_mvpMatrix, false, mvpMatrix.elements); // 清除的顏色和深度緩衝 gl.clear(gl.COLOR_BUFFER_BIT | gl.DEPTH_BUFFER_BIT); gl.drawArrays(gl.TRIANGLES, 0, n); // Draw the triangles // Prepare the model matrix for another pair of triangles modelMatrix.setTranslate(-0.75, 0, 0); // Calculate the model view projection matrix mvpMatrix.set(projMatrix).multiply(viewMatrix).multiply(modelMatrix); // Pass the model view projection matrix to u_MvpMatrix gl.uniformMatrix4fv(u_mvpMatrix, false, mvpMatrix.elements); gl.drawArrays(gl.TRIANGLES, 0, n); // Draw the triangles } function initVertexBuffers(gl) { //在這裡你會看到三角形的位置不是按順序排列的 var verticesColors = new Float32Array([ //頂點座標和顏色 0.0, 1.0, -2.0, 1.0, 1.0, 0.4, // 先繪製黃色三角形，設定在中間 -0.5, -1.0, -2.0, 1.0, 1.0, 0.4, 0.5, -1.0, -2.0, 1.0, 0.4, 0.4, 0.0, 1.0, 0.0, 0.4, 0.4, 1.0, // 設定藍色三角形在最前面 -0.5, -1.0, 0.0, 0.4, 0.4, 1.0, 0.5, -1.0, 0.0, 0.4, 0.4, 1.0, 0.0, 1.0, -4.0, 0.4, 1.0, 0.4, // 設定綠色三角形在最後面 -0.5, -1.0, -4.0, 0.4, 1.0, 0.4, 0.5, -1.0, -4.0, 0.4, 1.0, 0.4, ]); var n = 9; // 建立緩衝區物件 var vertexColorbuffer = gl.createBuffer(); if (!vertexColorbuffer) { console.log('Failed to create the buffer object'); return -1; } // 繫結緩衝區物件並將頂點資訊寫入緩衝帶 gl.bindBuffer(gl.ARRAY_BUFFER, vertexColorbuffer); gl.bufferData(gl.ARRAY_BUFFER, verticesColors, gl.STATIC_DRAW); var FSIZE = verticesColors.BYTES_PER_ELEMENT; // Assign the buffer object to a_Position and enable the assignment 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, 3, gl.FLOAT, false, FSIZE * 6, 0); gl.enableVertexAttribArray(a_Position); // Assign the buffer object to a_Color and enable the assignment var a_Color = gl.getAttribLocation(gl.program, 'a_Color'); if(a_Color < 0) { console.log('Failed to get the storage location of a_Color'); return -1; } gl.vertexAttribPointer(a_Color, 3, gl.FLOAT, false, FSIZE * 6, FSIZE * 3); gl.enableVertexAttribArray(a_Color); // Unbind the buffer object gl.bindBuffer(gl.ARRAY_BUFFER, null); return n; }