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根据教程：ogldev一步步从零开始，记录学习历程 一、索引绘制我们之前使用glDrawArrays()函数绘制了一个三角形，属于顺序绘制，即从指定的偏移量依次扫描顶点缓冲区所有图元的每一个顶点。 正如下图，我们绘制一个三角形只需要指定三个顶点即可，但是如果绘制两个三角形组成的一个平行四边形就需要六个顶点，而且会有两个顶点相重叠：
可以看到顶点V2和V3在顶点缓冲区会出现两次，如果我们的图形更复杂一些呢？顶点重复的现象会更多 如果我们引入一个索引缓冲例如下图：
顶点缓冲区内只放四个顶点，而我们用六个索引就可以表示出按照V1V2V3V4V2V3顺序绘制图形 二、代码解释 2.1 opengl_math.h: #ifndef __OPENGL_MATH_H #define __OPENGL_MATH_H #include #include #define PI (3.14159265358979323846) #define PI_DIV_180 (0.017453292519943296) #define INV_PI_DIV_180 (57.2957795130823229) #define DegToRad(x) ((x)*PI_DIV_180) #define RadToDeg(x) ((x)*INV_PI_DIV_180) //向量 typedef float Vector3f[3]; //向量赋值 inline void LoadVector3(Vector3f v, const float x, const float y, const float z) { v[0] = x; v[1] = y; v[2] = z; } //缩放向量 inline void ScaleVector3(Vector3f v, const float scale) { v[0] *= scale; v[1] *= scale; v[2] *= scale; } // 4 * 4 矩阵： // 0 4 8 12 // 1 5 9 13 // 2 6 10 14 // 3 7 11 15 typedef float Matrix44f[16]; //4*4单位矩阵 inline void LoadIdentity44(Matrix44f m) { m[0] = 1.0f; m[4] = 0.0f; m[8] = 0.0f; m[12] = 0.0f; m[1] = 0.0f; m[5] = 1.0f; m[9] = 0.0f; m[13] = 0.0f; m[2] = 0.0f; m[6] = 0.0f; m[10] = 1.0f; m[14] = 0.0f; m[3] = 0.0f; m[7] = 0.0f; m[11] = 0.0f; m[15] = 1.0f; } //4*4矩阵相乘 inline void MatrixMultiply44(Matrix44f product, const Matrix44f a, const Matrix44f b) { unsigned int j, k; for (unsigned int i = 0; i < 16; i++) { j = i % 4; k = i / 4 * 4; product[i] = a[j] * b[k] + a[j + 4] * b[k + 1] + a[j + 8] * b[k + 2] + a[j + 12] * b[k + 3]; } } //缩放变换 inline void ScaleMatrix44(Matrix44f m, float xScale, float yScale, float zScale) { LoadIdentity44(m); m[0] = xScale; m[5] = yScale; m[10] = zScale; } //旋转变换 inline void RotationMatrix44(Matrix44f m, float angle, float x, float y, float z) { LoadIdentity44(m); if (z == 1)//绕z轴 { m[0] = cosf(angle); m[4] = -sinf(angle); m[1] = sinf(angle); m[5] = cosf(angle); } else if (y == 1)//绕y轴 { m[0] = cosf(angle); m[8] = -sinf(angle); m[2] = sinf(angle); m[10] = cosf(angle); } else if (x == 1)//绕x轴 { m[5] = cosf(angle); m[9] = -sinf(angle); m[6] = sinf(angle); m[10] = cosf(angle); } } inline void RotationMatrix44(Matrix44f m, float RotateX, float RotateY, float RotateZ) { Matrix44f rx, ry, rz, temp; const float x = DegToRad(RotateX); const float y = DegToRad(RotateY); const float z = DegToRad(RotateZ); RotationMatrix44(rx, x, 1, 0, 0); RotationMatrix44(ry, y, 0, 1, 0); RotationMatrix44(rz, z, 0, 0, 1); MatrixMultiply44(temp, rz, ry); MatrixMultiply44(m,temp, rx); } //平移变换 inline void TranslationMatrix44(Matrix44f m, float x, float y, float z) { LoadIdentity44(m); m[12] = x; m[13] = y; m[14] = z; } #endif3d数学头文件没有进行改变，因为本节主要是增加了索引绘制，不涉及数学上的多余操作 2.2 main.c #include #include #include #include #include #include #include #include "opengl_math.h" using namespace std; GLuint VBO; GLuint gWorldLocation; GLuint IBO; const char* pVSFileName = "shader.vs"; const char* pFSFileName = "shader.fs"; bool ReadFile(const char* pFileName, string &outFile) { ifstream f(pFileName); bool ret = FALSE; if (f.is_open()) { string line; while (getline(f, line)) { outFile.append(line); outFile.append("\n"); } f.close(); ret = TRUE; } else { fprintf(stderr, "%s:%d: unable to opem file '%s'\n", __FILE__, __LINE__, pFileName); system("pause"); } return ret; } static void Render() { glClear(GL_COLOR_BUFFER_BIT); static float Scale = 0.0f; Scale += 0.001f; Matrix44f World; RotationMatrix44(World, Scale, 0, 1, 0); glUniformMatrix4fv(gWorldLocation, 1, GL_FALSE, &World[0]); glEnableVertexAttribArray(0); glBindBuffer(GL_ARRAY_BUFFER, VBO); glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 0, 0); //绘制前绑定索引缓冲 glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, IBO); //索引绘制图形 glDrawElements(GL_TRIANGLES, 12, GL_UNSIGNED_INT, 0); glDisableVertexAttribArray(0); glutSwapBuffers(); } static void InitializeGlutCallbacks() { glutDisplayFunc(Render); glutIdleFunc(Render); } static void CreateVertexBuffer() { Vector3f Vertices[4]; LoadVector3(Vertices[0], -1.0f, -1.0f, 0.0f); LoadVector3(Vertices[1], 0.0f, -1.0f, 1.0f); LoadVector3(Vertices[2], 1.0f, -1.0f, 0.0f); LoadVector3(Vertices[3], 0.0f, 1.0f, 0.0f); glGenBuffers(1, &VBO); glBindBuffer(GL_ARRAY_BUFFER, VBO); glBufferData(GL_ARRAY_BUFFER, sizeof(Vertices), Vertices, GL_STATIC_DRAW); } static void CreateIndexBuffer() { GLuint Indices[] = { 0,3,1, 1,3,2, 2,3,0, 0,1,2}; glGenBuffers(1, &IBO); glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, IBO); glBufferData(GL_ELEMENT_ARRAY_BUFFER, sizeof(Indices), Indices, GL_STATIC_DRAW); } static void AdderShader(GLuint ShaderProgram, const char* ShaderText, GLenum ShaderType) { GLuint ShaderObj = glCreateShader(ShaderType); if (!ShaderObj) { fprintf(stderr, "Error creating shader type %d\n", ShaderType); exit(1); } const GLchar* p[1]; p[0] = ShaderText; GLint Lengths[1]; Lengths[0] = strlen(ShaderText); glShaderSource(ShaderObj, 1, p, Lengths); glCompileShader(ShaderObj); GLint success; glGetShaderiv(ShaderObj, GL_COMPILE_STATUS, &success); if (!success) { GLchar InfoLog[1024]; glGetShaderInfoLog(ShaderObj, 1024, NULL, InfoLog); fprintf(stderr, "Error compiling shader type %d: '%s'\n", ShaderType, InfoLog); system("pause"); exit(1); } glAttachShader(ShaderProgram, ShaderObj); } static void CompilerShader() { GLuint ShaderProgram = glCreateProgram(); if (ShaderProgram == 0) { fprintf(stderr, "Error creating shader program\n"); exit(1); } string vs, fs; if (!ReadFile(pVSFileName,vs)) { exit(1); } if (!ReadFile(pFSFileName,fs)) { exit(1); } AdderShader(ShaderProgram,vs.c_str(),GL_VERTEX_SHADER); AdderShader(ShaderProgram,fs.c_str(), GL_FRAGMENT_SHADER); GLint Success = 0; GLchar ErrorLog[1024] = { 0 }; glLinkProgram(ShaderProgram); glGetProgramiv(ShaderProgram, GL_LINK_STATUS, &Success); if (!Success) { glGetProgramInfoLog(ShaderProgram, sizeof(ErrorLog), NULL, ErrorLog); fprintf(stderr, "Error linking shader program: '%s'\n", ErrorLog); system("pause"); exit(1); } glValidateProgram(ShaderProgram); glGetProgramiv(ShaderProgram, GL_VALIDATE_STATUS, &Success); if (!Success) { glGetProgramInfoLog(ShaderProgram, sizeof(ErrorLog), NULL, ErrorLog); fprintf(stderr, "Invalid shader program: '%s'\n", ErrorLog); system("pause"); exit(1); } glUseProgram(ShaderProgram); gWorldLocation = glGetUniformLocation(ShaderProgram, "gWorld"); assert(gWorldLocation != 0xFFFFFFFF); } int main(int argc, char **argv) { glutInit(&argc, argv); glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGBA); glutInitWindowPosition(10, 10); glutInitWindowSize(1024, 768); glutCreateWindow("Index"); InitializeGlutCallbacks(); GLenum res = glewInit(); if (res != GLEW_OK) { fprintf(stderr, "Error:'%s'\n", glewGetErrorString(res)); system("pause"); return 1; } printf("GL version: %s \n", glGetString(GL_VERSION)); glClearColor(0.0f, 0.0f, 0.0f, 0.0f); CreateVertexBuffer(); CreateIndexBuffer(); CompilerShader(); glutMainLoop(); return 0; }这里增加了索引绘制的相关代码 2.2.1 创建顶点缓冲区 Vector3f Vertices[4]; LoadVector3(Vertices[0], -1.0f, -1.0f, 0.0f); LoadVector3(Vertices[1], 0.0f, -1.0f, 1.0f); LoadVector3(Vertices[2], 1.0f, -1.0f, 0.0f); LoadVector3(Vertices[3], 0.0f, 1.0f, 0.0f); glGenBuffers(1, &VBO); glBindBuffer(GL_ARRAY_BUFFER, VBO); glBufferData(GL_ARRAY_BUFFER, sizeof(Vertices), Vertices, GL_STATIC_DRAW);这里在顶点缓冲区里添加了四个顶点数据，想要绘制一个三棱锥，如果看不懂这里的代码请移步教程： OpenGL学习之路2----画一个点 2.2.2 创建索引缓冲器 GLuint Indices[] = { 0,3,1, 1,3,2, 2,3,0, 0,1,2}; glGenBuffers(1, &IBO); glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, IBO); glBufferData(GL_ELEMENT_ARRAY_BUFFER, sizeof(Indices), Indices, GL_STATIC_DRAW); 先是定义一个索引数组，存放与顶点缓冲区中相匹配的位置索引 IBO是GLuint类型的全局变量，作为索引缓冲区对象的引用句柄 GLuint IBO; 跟创建顶点缓冲器一样，创建索引缓冲器先调用glGenBuffers()返回未使用的缓存对象的名称，再调用glBindBuffer()激活对象，最后使用glBufferData()函数把索引的信息绑定在IBO对象上 唯一不同的是再调用glBindBuffer()函数和glBufferData()函数的缓存对象类型是GL_ELEMENT_ARRAY_BUFFER 2.2.3 使用索引绘制图形渲染函数Render()中，不再用glDrawArrays()来绘制图形，而是用glDrawElements()用索引绘制图形 glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, IBO); glDrawElements(GL_TRIANGLES, 12, GL_UNSIGNED_INT, 0); 使用索引缓冲之前需要用glBindBuffer()来绑定索引缓冲，每次使用缓冲时都要先进行绑定这点在之前的学习中已经提到过了 void glDrawElements (GLenum mode, GLsizei count , GLenum type,const GLvoid *indices );使用count个元素来定义一系列几何图元，这里一共是12个索引共绘制12个顶点所以是12 indices定义了元素数组缓存中的偏移地址，这里索引数组是顺序存储没有偏移值所以为0 mode必须是图元类型的标识符：比如GL_TRIANGLES、GL_LINE_LOOP、GL_LINES、GL_POINTS，这里绘制三角形所以是GL_TRIANGLES type必须是GL_UNSIGNED_BYTE, GL_UNSIGNED_SHORT或者GL_UNSIGNED_INT当中一个,索引数组数据类型为GLuint所以是GL_UNSIGNED_INT 2.3 着色器shader.vs: #version 330 layout (location = 0) in vec3 Position; uniform mat4 gWorld; out vec4 Color; void main() { gl_Position = gWorld * vec4(Position,1.0); Color = vec4(clamp(Position,0.0,1.0),1.0); }shader.fs: #version 330 in vec4 Color; out vec4 FragColor; void main() { FragColor = Color; }都没有变化，因为这节只是添加索引绘制相关代码，着色器代码跟上一节相同 三、运行结果
可以看到颜色渐变的三棱锥，围绕着y轴进行旋转，如果不理解为何颜色渐变或者旋转请移步教程： OpenGL学习之路6----平移，旋转和缩放变换 OpenGL学习之路7----插值 |
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