shader学习笔记五： 访问纹理坐标数据

关键代码：

	string vsCode  =   "uniform vec4 _color;\
						varying vec4 outColor;\
						void main()\
						{\
							outColor    =   _color;\
							gl_TexCoord[0]  =   gl_MultiTexCoord0;\
							gl_Position =   gl_ModelViewProjectionMatrix * gl_Vertex;\
						}";

	string psCode  = "varying vec4 outColor;\
					  uniform     sampler2D   _texture;\
					  void main()\
					  {\
					  	  vec4 color   =   texture2D(_texture, gl_TexCoord[0].st);\
						  gl_FragColor    =   color;\
					  }";

    //gl_TexCoord[0]  =   gl_MultiTexCoord0;; 表示接收opengl传过来的纹理坐标
	//gl_TexCoord是输出，输出到ps里 ，在ps中不可直接使用 gl_MultiTexCoord0  当前版本的opengl每个顶点有八组纹理坐标 gl_TexCoord[0~7] gl_MultiTexCoord0~7
	//uniform  sampler2D  _texture;  sampler2D变量 只能在PS里 不能放到vs中，可以理解为二维图片，或者叫二维纹理
	//texture2D() 内置函数，用于根据纹理及坐标获取纹理颜色

代码例子：

main.cpp

/*
*
* 该实例演示访问纹理坐标数据
*
*/

#define GLEW_STATIC
#include 
#include 
#include 
#include 

#include 
#include 

#include  // glm::vec3
#include  // glm::vec4
#include  // glm::mat4
#include  // glm::translate, glm::rotate, glm::scale
#include 

#include "FreeImage.h"

#include "shader.hpp"

#pragma comment(linker, "/subsystem:\"windows\" /entry:\"mainCRTStartup\"" )  //这行是取消显示控制台

char szTitle[64] = "opengl view";


//glm::vec4 vec(1.0f, 0.0f, 0.0f, 1.0f);//创建一个点
//glm::mat4 trans = glm::mat4(1.0f);//创建单位矩阵
//Window dimensions    
const GLuint WIDTH = 800, HEIGHT = 600;

GLfloat ratio = 1.f;
GLfloat xpos, ypos;

glm::vec3 _eye(0, 0, 10);
glm::vec3 _lookAt(0, 0, 0);
glm::vec3 _up(0, 1, 0);

glm::mat4 _matProj = glm::mat4(1.0f);//创建单位矩阵
glm::mat4 _matView = glm::mat4(1.0f);//创建单位矩阵


float size = 100.0f;

//顶点数据
struct Vertex {
	float x, y, z;
	float u, v;
};

Vertex g_cubeVertices[] =
{
	{ -1.0f, -1.0f, 1.0f, 0.0f, 0.0f },
	{ 1.0f, -1.0f, 1.0f, 1.0f, 0.0f },
	{ 1.0f, 1.0f, 1.0f, 1.0f, 1.0f },
	{ -1.0f, 1.0f, 1.0f, 0.0f, 1.0f },

	{ -1.0f, -1.0f, -1.0f, 1.0f, 0.0f },
	{ -1.0f, 1.0f, -1.0f, 1.0f, 1.0f },
	{ 1.0f, 1.0f, -1.0f, 0.0f, 1.0f },
	{ 1.0f, -1.0f, -1.0f, 0.0f, 0.0f },

	{ -1.0f, 1.0f, -1.0f, 0.0f, 1.0f },
	{ -1.0f, 1.0f, 1.0f, 0.0f, 0.0f },
	{ 1.0f, 1.0f, 1.0f, 1.0f, 0.0f },
	{ 1.0f, 1.0f, -1.0f, 1.0f, 1.0f },

	{ -1.0f, -1.0f, -1.0f, 1.0f, 1.0f },
	{ 1.0f, -1.0f, -1.0f, 0.0f, 1.0f },
	{ 1.0f, -1.0f, 1.0f, 0.0f, 0.0f },
	{ -1.0f, -1.0f, 1.0f, 1.0f, 0.0f },

	{ 1.0f, -1.0f, -1.0f, 1.0f, 0.0f },
	{ 1.0f, 1.0f, -1.0f, 1.0f, 1.0f },
	{ 1.0f, 1.0f, 1.0f, 0.0f, 1.0f },
	{ 1.0f, -1.0f, 1.0f, 0.0f, 0.0f },

	{ -1.0f, -1.0f, -1.0f, 0.0f, 0.0f },
	{ -1.0f, -1.0f, 1.0f, 1.0f, 0.0f },
	{ -1.0f, 1.0f, 1.0f, 1.0f, 1.0f },
	{ -1.0f, 1.0f, -1.0f, 0.0f, 1.0f },

	// 地面数据
	{ -size, -1.0f, -size, 0.0f, 0.0f },
	{ -size, -1.0f, size, 100.0f, 0.0f },
	{ size, -1.0f, size, 100.0f, 100.0f },
	{ size, 0.0f, -size, 0.0f, 100.0f }
};

//纹理ID
GLuint  _texture;
GLuint  _vbo;

//地面纹理
GLuint  _texGround;

Shader* _shader = nullptr;


static void error_callback(int error, const char* description) {
	fputs(description, stderr);
}

static void key_callback(GLFWwindow* window, int key, int scancode, int action, int mods) {
	std::cout << "key " << key << std::endl;

	switch(key) {
		case GLFW_KEY_ESCAPE:
			glfwSetWindowShouldClose(window, GL_TRUE);
			break;
		case GLFW_KEY_UP:
			_eye.z  -=  0.1f;   //这里修改摄像机参数
			break;
		case GLFW_KEY_DOWN:
			_eye.z  +=  0.1f;
			break;
		case GLFW_KEY_RIGHT:
			_eye.x  -=  1.0f;
			break;
		case GLFW_KEY_LEFT:
			_eye.x  +=  1.0f;
			break;

		default:
			break;
	}
}

static void mouse_button_callback(GLFWwindow* window, int button, int action, int mods) {
	if(action != GLFW_PRESS)
		return;

	switch(button) {
		case GLFW_MOUSE_BUTTON_LEFT:
			std::cout << "Mosue left button clicked!" << std::endl;
			break;
		case GLFW_MOUSE_BUTTON_MIDDLE:
			std::cout << "Mosue middle button clicked!" << std::endl;
			break;
		case GLFW_MOUSE_BUTTON_RIGHT:
			std::cout << "Mosue right button clicked!" << std::endl;
			break;
		default:
			return;
	}
	return;
}

static void cursor_position_callback(GLFWwindow* window, double x, double y) {
	//std::cout << "Mouse position move to X: " << x << " Y: " << y << std::endl;
	xpos = float((x - WIDTH / 2) / WIDTH) * 2;
	ypos = float(0 - (y - HEIGHT / 2) / HEIGHT) * 2;
	return;
}

static void scroll_callback(GLFWwindow* window, double x, double y) {
	return;
}

static unsigned createTexture(int w, int h, const void* data, GLenum type) {
	unsigned    texId;
	glGenTextures(1, &texId);
	glBindTexture(GL_TEXTURE_2D, texId);
	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);

	glTexImage2D(GL_TEXTURE_2D, 0, type, w, h, 0, type, GL_UNSIGNED_BYTE, data);

	return  texId;
}
/**
*   使用FreeImage加载图片
*/
static unsigned createTextureFromImage(const char* fileName) {
	//1 获取图片格式
	FREE_IMAGE_FORMAT fifmt = FreeImage_GetFileType(fileName, 0);
	if(fifmt == FIF_UNKNOWN) {
		return  0;
	}
	//2 加载图片
	FIBITMAP    *dib = FreeImage_Load(fifmt, fileName, 0);

	FREE_IMAGE_COLOR_TYPE type = FreeImage_GetColorType(dib);

	//3 获取数据指针
	FIBITMAP*   temp = dib;
	dib = FreeImage_ConvertTo32Bits(dib);
	FreeImage_Unload(temp);

	BYTE*   pixels = (BYTE*)FreeImage_GetBits(dib);
	int     width = FreeImage_GetWidth(dib);
	int     height = FreeImage_GetHeight(dib);

	for(int i = 0; i < width * height * 4; i += 4) {
		BYTE temp = pixels[i];
		pixels[i] = pixels[i + 2];
		pixels[i + 2] = temp;
	}

	unsigned    res = createTexture(width, height, pixels, GL_RGBA);
	FreeImage_Unload(dib);
	return      res;
}

static GLint _colorID;
static GLint _textureID;


static void onInit() {
	_texture    =   createTextureFromImage("../res/1.jpg");
	_texGround  =   createTextureFromImage("../res/dimian.jpg");

	glGenBuffers(1, &_vbo);
	glBindBuffer(GL_ARRAY_BUFFER, _vbo);
	glBufferData(GL_ARRAY_BUFFER, sizeof(g_cubeVertices), g_cubeVertices, GL_STATIC_DRAW);
	glBindBuffer(GL_ARRAY_BUFFER, 0);


	string vsCode  =   "uniform vec4 _color;\
						varying vec4 outColor;\
						void main()\
						{\
							outColor    =   _color;\
							gl_TexCoord[0]  =   gl_MultiTexCoord0;\
							gl_Position =   gl_ModelViewProjectionMatrix * gl_Vertex;\
						}";

	string psCode  = "varying vec4 outColor;\
					  uniform     sampler2D   _texture;\
					  void main()\
					  {\
					  	  vec4 color   =   texture2D(_texture, gl_TexCoord[0].st);\
						  gl_FragColor    =   color;\
					  }";

    //gl_TexCoord[0]  =   gl_MultiTexCoord0;; 表示接收opengl传过来的纹理坐标
	//gl_TexCoord是输出，输出到ps里 ，在ps中不可直接使用 gl_MultiTexCoord0  当前版本的opengl每个顶点有八组纹理坐标 gl_TexCoord[0~7] gl_MultiTexCoord0~7
	//uniform  sampler2D  _texture;  sampler2D变量 只能在PS里 不能放到vs中，可以理解为二维图片，或者叫二维纹理
	//texture2D() 内置函数，用于根据纹理及坐标获取纹理颜色
	
	//_shader = new Shader("../res/shader/vertShader1.vert", "../res/shader/fragShader1.frag");

	_shader = new Shader(vsCode, psCode, true);

	//获取shader中的uniform vec4 _color 地址，即建立shader中的变量和程序中变量关联
	_colorID  =   _shader->getUniformLocation("_color");
	//获取shader中的uniform sampler2D _texture 地址，即建立shader中的变量和程序中变量关联
	_textureID = _shader->getUniformLocation("_texture");
}

static void onDestory() {
	glDeleteTextures(1, &_texture);
	glDeleteTextures(1, &_texGround);
	glDeleteBuffers(1, &_vbo);   //删除VBO 显存中释放VBO内存
}

// 绘制
static void render(GLFWwindow * window) {

	glClearColor(0, 0, 0, 1);
	glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

	glEnable(GL_DEPTH_TEST);
	glEnable(GL_TEXTURE_2D);

	glMatrixMode(GL_MODELVIEW);
	_matView = glm::lookAt(_eye, _lookAt, _up); //使用glm数学库 根据公式计算得到视图矩阵  这公式可以推倒出来

	//摄像机围绕目标旋转
	static float angle = 0; //旋转角度
	float r = 10;           //旋转半径
	_eye.x = cos(angle * glm::pi<double>() / 180) * r;
	_eye.z = sin(angle * glm::pi<double>() / 180) * r;
	angle += 1;  //角度每帧加一

	glm::mat4 matVP = _matProj * _matView;
	glLoadMatrixf(&matVP[0][0]);

	
	glBindTexture(GL_TEXTURE_2D, _texture); //该函数表示把纹理放到第0个纹理单元

	glEnableClientState(GL_VERTEX_ARRAY);
	glEnableClientState(GL_TEXTURE_COORD_ARRAY);
	//开始使用ID为 _vbo  的buffer 接下来的操作针对这个VBO
	glBindBuffer(GL_ARRAY_BUFFER, _vbo);

	float* addrVertex = (float*)0;
	float* uvAddress = (float*)12;

	glVertexPointer(3, GL_FLOAT, sizeof(Vertex), addrVertex);
	glTexCoordPointer(2, GL_FLOAT, sizeof(Vertex), uvAddress);

	// 绘制 立方体
	_shader->begin(); //使用 shader 对绘制立方体起作用

	//先begin 使用这个shader 然后才能修改
	glUniform4f(_colorID, 0, 1, 1, 1); //通过_colorID 改变对应的shader中 _color 的值
	glUniform1i(_textureID, 0); //该函数表示shader程序纹理数据从第0个纹理单元取， opengl 当前版本一个顶点有八个纹理单元， glBindTexture(GL_TEXTURE_2D, _texture);//该函数设置了第0个纹理单元纹理数据

	glDrawArrays(GL_QUADS, 0, 24);   //shader 只在针对 glDrawArrays 这类绘制函数其作用，顶点处理阶段调用顶点shader 光栅化处理阶段调用片元shader
	_shader->end();   //结束  如果不掉用这个函数 glUseProgram设置为0，这个shader程序会对后面的绘制产生影响

	//绘制地面
	//glLoadIdentity(); //这里打开 地面就不会跟着旋转 说明摄像机操作的是模型矩阵
	glBindTexture(GL_TEXTURE_2D, _texGround);
	glDrawArrays(GL_QUADS, 24, 4);

	glDisableClientState(GL_VERTEX_ARRAY);
	glDisableClientState(GL_TEXTURE_COORD_ARRAY);
	glBindTexture(GL_TEXTURE_2D, 0);
	glfwSwapBuffers(window);
	glfwPollEvents();
}

int main(void) {
	GLFWwindow * window;

	glfwSetErrorCallback(error_callback);

	if(!glfwInit())
		return -1;

	window = glfwCreateWindow(WIDTH, HEIGHT, szTitle, NULL, NULL);
	if(!window) {
		glfwTerminate();
		exit(EXIT_FAILURE);
	}

	glfwSetKeyCallback(window, key_callback);
	glfwSetMouseButtonCallback(window, mouse_button_callback);
	glfwSetCursorPosCallback(window, cursor_position_callback);
	glfwSetScrollCallback(window, scroll_callback);

	glfwMakeContextCurrent(window);

	glewExperimental = GL_TRUE;
	glewInit();
	onInit();
	glViewport(0, 0, WIDTH, HEIGHT); //设置opengl视口 即看到的显示区域

	_matProj = glm::perspective(glm::radians(60.0f), float(WIDTH) / float(HEIGHT), 0.1f, 1000.0f);//使用glm数学库 根据公式计算得到投影矩阵  这公式可以推倒出来

	while(!glfwWindowShouldClose(window)) {
		render(window);
	}

	onDestory();
	glfwDestroyWindow(window);

	glfwTerminate();
	return 0;
}

运行结果：