实现步骤
第一步：设置所需要的OpenGL环境
设置上下文环境
删除已经存在的渲染的缓存
设置颜色缓存
设置帧缓存
清除缓存
设置窗口大小
开启功能
编译shander
使用program
获取shader中的属性和uniform索引
第二步：绘制图片
获取图片数据并且的到对应的纹理id
指定纹理，绑定纹理
开始对图形进行渲染
(
启用顶点属性数组纹理坐标，将纹理坐标传递到shader中
启用顶点属性数组顶点坐标，将顶点坐标传递到shader中
启用索引数组
开始绘制
)
解绑纹理
实现
这次实现的过程有些艰难啊，走了很多的弯路，不过也因此学到蛮多的，自己写的怎么都运行不了，但是在别人的基础上运行就不行，其中错误的地方有：1.纹理的数据错误，使用png的库失败；2.绘制函数的参数错误；3.使用新版本的glsl语言版本，但是xcode并不支持，并不熟悉期间的语言版本迭代；
实现代码：
主程序
#include "SOIL.h"
static void error_callback(int error, const char* description)
{
fprintf(stderr, "Error: %s\n", description);
}
int main(void)
{
GLFWwindow* window;
glfwSetErrorCallback(error_callback);
if (!glfwInit())
exit(EXIT_FAILURE);
window = glfwCreateWindow(640, 480, "Simple example", NULL, NULL);
if (!window)
{
std::cout << "Failed to create GLFW window" << std::endl;
glfwTerminate();
exit(EXIT_FAILURE);
}
glfwMakeContextCurrent(window);
glewExperimental = GL_TRUE;
glewInit();
glfwSwapInterval(1);
glViewport(0, 0, 640, 480);
bool ret = getImageData("/Users/staff/Desktop/Moni/Moni/wall.png");
if (!ret) {
cout << "get iamge data is failed." << endl;
}
else {
cout << "get iamge data is success." << endl;
//测试图片数据
// FILE * file;
// file = fopen("/Users/staff/Desktop/abc.png","wb");
// if (file)
// {
// fwrite(_sp_image_data.getBytes(),1,_sp_image_data.getSize(), file);
// }
// fclose(file);
}
// 第一行和第三行不是严格必须的，默认使用GL_TEXTURE0作为当前激活的纹理单元
/**
* GL_TEXTURE_2D表示操作2D纹理
* 创建纹理对象，
* 绑定纹理对象，
*/
glPixelStorei(GL_UNPACK_ALIGNMENT, 8);
glGenTextures(1, &_sp_textureID);
glBindTexture(GL_TEXTURE_2D, _sp_textureID);
glTexParameteri( GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR );
glTexParameteri( GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR );
// glTexParameteri( GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE );
// glTexParameteri( GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE );
/**
* 将图像数据传递给到GL_TEXTURE_2D中, 因其于textureID纹理对象已经绑定，所以即传递给了textureID纹理对象中。
* glTexImage2d会将图像数据从CPU内存通过PCIE上传到GPU内存。
* 不使用PBO时它是一个阻塞CPU的函数，数据量大会卡
*/
// glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, _sp_image_size.getX(), _sp_image_size.getY(), 0, GL_RGBA, GL_UNSIGNED_BYTE, _sp_image_data.getBytes());
// glGenerateMipmap(GL_TEXTURE_2D);
int width, height;
unsigned char* image = SOIL_load_image("/Users/staff/Desktop/fgh/fgh/wall.jpg", &width, &height, 0, SOIL_LOAD_RGB);
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, width, height, 0, GL_RGB, GL_UNSIGNED_BYTE, image);
glGenerateMipmap(GL_TEXTURE_2D);
SOIL_free_image_data(image);
glBindTexture(GL_TEXTURE_2D, 0);
_vertexShader = glCreateShader(GL_VERTEX_SHADER);
glShaderSource(_vertexShader, 1, &CCPositionTextureColorVert, NULL);
glCompileShader(_vertexShader);
GLint status;
glGetShaderiv(_vertexShader, GL_COMPILE_STATUS, &status);
if (!status) {
GLint infoLen = 0;
glGetShaderiv(_vertexShader, GL_INFO_LOG_LENGTH, &infoLen);
if (infoLen) {
char* infoLog = static_cast<char *>(malloc(sizeof(char) * infoLen));
glGetShaderInfoLog(_vertexShader, infoLen, NULL, infoLog);
cout << "compile vert shader wrong..." << infoLog << endl;
}
}
else {
cout << "compile vert shader success..." << endl;
}
_fragShader = glCreateShader(GL_FRAGMENT_SHADER);
glShaderSource(_fragShader, 1, &CCPositionTextureColorFrag, NULL);
glCompileShader(_fragShader);
glGetShaderiv(_fragShader, GL_COMPILE_STATUS, &status);
if (!status) {
GLint infoLen = 0;
glGetShaderiv(_fragShader, GL_INFO_LOG_LENGTH, &infoLen);
if (infoLen) {
char* infoLog = static_cast<char *>(malloc(sizeof(char) * infoLen));
glGetShaderInfoLog(_fragShader, infoLen, NULL, infoLog);
cout << "compile frag shader wrong..." << infoLog << endl;
}
}
else {
cout << "compile vert frag success..." << endl;
}
_program = glCreateProgram();
glAttachShader(_program, _vertexShader);
glAttachShader(_program, _fragShader);
glLinkProgram(_program);
glGetProgramiv(_program, GL_LINK_STATUS, &status);
if (status == GL_FALSE) {
GLint infoLen = 0;
glGetProgramiv(_program, GL_INFO_LOG_LENGTH, &infoLen);
if (infoLen) {
char* infoLog = static_cast<char *>(malloc(sizeof(char) * infoLen));
glGetProgramInfoLog(_program, infoLen, NULL, infoLog);
cout << "link program wrong..." << infoLog << endl;
}
}
else {
cout << "the program link success." << endl;
}
//设置顶点数据（和缓冲）和属性指针
GLfloat vertices[] = {
// Positions // Colors // Texture Coords
0.5f, 0.5f, 0.0f, 1.0f, 0.0f, 0.0f, 2.0f, 0.1f,
0.5f, -0.5f, 0.0f, 0.0f, 1.0f, 0.0f, 2.0f, 0.8f,
-0.5f, -0.5f, 0.0f, 0.0f, 0.0f, 1.0f, 0.5f, 0.8f,
-0.5f, 0.5f, 0.0f, 1.0f, 1.0f, 0.0f, 0.5f, 0.1f
};
GLuint indices[] = {
0, 1, 3,
1, 2, 3
};
GLuint VBO, VAO, EBO;
glGenVertexArrays(1, &VAO);
glGenBuffers(1, &VBO);
glGenBuffers(1, &EBO);
glBindVertexArray(VAO);
glBindBuffer(GL_ARRAY_BUFFER, VBO);
glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW);
glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, EBO);
glBufferData(GL_ELEMENT_ARRAY_BUFFER, sizeof(indices), indices, GL_STATIC_DRAW);
GLuint _positionSlot = glGetAttribLocation(_program, "position");
GLuint _colorSlot = glGetAttribLocation(_program, "color");
GLuint _textureCoordsSlot = glGetAttribLocation(_program, "texCoord");
//GLuint _textureSlot = glGetUniformLocation(shader.program, "ourTexture");
glVertexAttribPointer(_positionSlot, 3, GL_FLOAT, GL_FALSE, 8 * sizeof(GLfloat), (GLvoid*)0);
glEnableVertexAttribArray(_positionSlot);
glVertexAttribPointer(_colorSlot, 3, GL_FLOAT, GL_FALSE, 8 * sizeof(GLfloat), (GLvoid*)(3 * sizeof(GLfloat)));
glEnableVertexAttribArray(_colorSlot);
glVertexAttribPointer(_textureCoordsSlot, 2, GL_FLOAT, GL_FALSE, 8 * sizeof(GLfloat), (GLvoid*)(6 * sizeof(GLfloat)));
glEnableVertexAttribArray(_textureCoordsSlot);
glBindVertexArray(0);
while (!glfwWindowShouldClose(window))
{
glfwPollEvents();
int width, height;
glfwGetFramebufferSize(window, &width, &height);
glViewport(0, 0, width, height);
glClearColor(0.2f, 0.3f, 0.3f, 1.0f);
glClear(GL_COLOR_BUFFER_BIT);
//use
glUseProgram(_program);
glEnable(GL_BLEND);
glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
glActiveTexture(GL_TEXTURE0);
glBindTexture(GL_TEXTURE_2D, _sp_textureID); // 绑定，即可从_textureID中取出图像数据
glUniform1i(glGetUniformLocation(_program, "ourTexture1"), 0);
//draw
glBindVertexArray(VAO);
glDrawElements(GL_TRIANGLES, 6, GL_UNSIGNED_INT, 0);
glBindVertexArray(0);
glfwPollEvents();
glfwSwapBuffers(window);
}
glDeleteVertexArrays(1, &VAO);
glDeleteBuffers(1, &VBO);
glDeleteBuffers(1, &EBO);
glfwDestroyWindow(window);
glfwTerminate();
exit(EXIT_SUCCESS);
}
上面是主程序的代码，除了这个，还需要顶点shader和片元shader；其实这里有个坑，就是glsl的语言版本，越望越后面，增加了更多的新 功能，导致我不认识，从而使用了新版本的，同时xcode只更新了到了2.0上，其他版本在xcode并不能使用，因此导编编译失败。
先是顶点shader：
const char* CCPositionTextureColorVert = STRINGIFY(
attribute vec3 position;
attribute vec3 color;
attribute vec2 texCoord;
varying vec3 ourColor;
varying vec2 TexCoord;
void main() {
gl_Position = vec4(position, 1.0);
ourColor = color;
TexCoord = texCoord;
}
);
接下来的是片元shader
const char* CCPositionTextureColorFrag = STRINGIFY(
varying vec3 ourColor;
varying vec2 TexCoord;
//varying vec4 color;
uniform sampler2D ourTexture1;
uniform sampler2D ourTexture2;
uniform float mixValue;
void main() {
gl_FragColor = mix(texture2D(ourTexture1, TexCoord) * vec4(ourColor, 1.0), texture2D(ourTexture2, vec2(-TexCoord.x, TexCoord.y)), mixValue);
}
);