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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 正確處理圖像的位置關係
如果沒有在上一節的基礎上把設置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，運行效果如下：
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="utf-8" />
<title>webgl第35課-深度緩衝之正確處理圖像的位置關係</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' +//模型視圖投影矩陣*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（開啓隱藏面消除功能）
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) {
//在這裏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，設置在中間
-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, // 設置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, // 設置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;
// 創建緩衝區對象
var vertexColorbuffer = gl.createBuffer();
if (!vertexColorbuffer) {
console.log('Failed to create the buffer object');
return -1;
}
// 綁定緩衝區對象並將頂點信息寫入緩衝帶
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;
}