前置：OpenGL基础11：空间
一、坐标系
我们都学过坐标系，根据z轴的方向，一般有两种不同的坐标系表示方法：
其中拇指是x轴正方向，食指是y轴正方向，中指是z轴正方形
OpenGL约定是右手坐标系，而在标准化设备坐标系(NDCSpace)中OpenGL使用的是左手坐标系
还记得上一章的这个公式嘛：
再看看下面的这个顶点着色器，是不是有种亲切感
#version 330 core
layout (location = 0) in vec3 position;
layout (location = 1) in vec4 color;
layout (location = 2) in vec2 texture;
out vec4 colorIn;
out vec2 texIn;
uniform mat4 model; //模型矩阵
uniform mat4 view; //观察矩阵
uniform mat4 projection; //投影矩阵
void main()
{
gl_Position = projection * view * model * vec4(position, 1.0);
colorIn = color;
texIn = vec2(texture.x, 1.0f - texture.y);
}
是的，我们将片段着色器修改如此，就至少可以开始生成我们想要的简单3D图形了
二、进入3D世界
依然是在 OpenGL基础8：SOIL库 这一章的代码上进行扩展，我们让那张拥有纹理的矩形在3D世界中“躺下”
效果如下：（有那种感觉了）
（顶点着色器在上面，片段着色器和Shader.h依旧不用改）
很明显可以看出来，我们用的投影方式是透视投影（近大远小）：
glm::mat4 projection = glm::mat4(1.0f);
projection = glm::perspective(glm::radians(45.0f), (GLfloat)WIDTH / (GLfloat)HEIGHT, 0.1f, 100.0f);
GLint projLoc = glGetUniformLocation(shaderYellow.Program, "projection");
glUniformMatrix4fv(projLoc, 1, GL_FALSE, glm::value_ptr(projection));
而对于模型，我们让它倾斜了一定的角度（向后倾倒55°）：
glm::mat4 model = glm::mat4(1.0f);
model = glm::rotate(model, glm::radians(-55.0f), glm::vec3(1.0f, 0.0f, 0.0f));
GLint modelLoc = glGetUniformLocation(shaderYellow.Program, "model");
glUniformMatrix4fv(modelLoc, 1, GL_FALSE, glm::value_ptr(model));
如果我们不设观察矩阵，那么我们相当于就是在(0, 0, 0)这个位置观察世界，然而问题就来了，我们的这个矩形中心点正是(0, 0, 0)，如果这样的话就会出现我们的“眼睛”和这个矩形过于近甚至重叠的情况
如果你玩过不少游戏，想象一下你卡了BUG，进入了游戏的某块箱子又或者是卡进了墙中，那么你就会发现你的视线可以直接穿过这面墙，这正是因为透视矩阵的near值设置大小超过了你与物体的距离
我们当然要避免这种情况，当然不是为了避免卡BUG，而是“往后退”，暂时定死在(0, 0, 3)的这个位置观察我们例子中的矩形，为什么这里说是“暂时定死”呢，因为我们肯定是在移动中观察世界的，后面我们也可以让“摄像机”动起来
也可以这样理解：观察矩阵即是摄像机的位置！但是由于相对关系，这个位置必然是是取反后的结果
因此我们的观察矩阵设置如下：
glm::mat4 view = glm::mat4(1.0f);
view = glm::translate(view, glm::vec3(0.0f, 0.0f, -3.0f));
GLint viewLoc = glGetUniformLocation(shaderYellow.Program, "view");
glUniformMatrix4fv(viewLoc, 1, GL_FALSE, glm::value_ptr(view));
搞定，完整代码如下：
#include<iostream>
#include<opengl/glew.h>
#define GLEW_STATIC
#include<GLFW/glfw3.h>
#include<glm/glm.hpp>
#include<glm/gtc/matrix_transform.hpp>
#include<glm/gtc/type_ptr.hpp>
#include"Shader.h"
#include<opengl/freeglut.h>
#include<SOIL.h>
void key_callback(GLFWwindow* window, int key, int scancode, int action, int mode);
const GLuint WIDTH = 800, HEIGHT = 600;
int main()
{
glfwInit();
glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3);
glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 3);
glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);
glfwWindowHint(GLFW_RESIZABLE, GL_FALSE);
GLFWwindow* window = glfwCreateWindow(WIDTH, HEIGHT, "LearnOpenGL", nullptr, nullptr);
glfwMakeContextCurrent(window);
glfwSetKeyCallback(window, key_callback);
glewExperimental = GL_TRUE;
glewInit();
int width, height;
glfwGetFramebufferSize(window, &width, &height);
glViewport(0, 0, width, height);
Shader shaderYellow("VShader.txt", "FShaderY.txt");
GLfloat vertices[] =
{
-0.5f, -0.5f, 0.0f, 0.0f, 0.0f, 1.0f, 0.0f, 0.0f,
0.5f, -0.5f, 0.0f, 0.0f, 1.0f, 0.0f, 1.0f, 0.0f,
-0.5f, 0.5f, 0.0f, 1.0f, 0.0f, 0.0f, 0.0f, 1.0f,
0.5f, 0.5f, 0.0f, 0.0f, 0.0f, 1.0f, 1.0f, 1.0f
};
GLuint indices[] =
{
0, 1, 2, //用前3个顶点绘制第一个三角形
1, 2, 3 //用后3个顶点绘制第二个三角形
};
GLuint VBO, EBO, VAO, texture;
glGenVertexArrays(1, &VAO);
glGenBuffers(1, &VBO);
glGenBuffers(1, &EBO);
glGenTextures(1, &texture);
glBindVertexArray(VAO);
glBindBuffer(GL_ARRAY_BUFFER, VBO);
glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, EBO);
glBindTexture(GL_TEXTURE_2D, texture);
glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW);
glBufferData(GL_ELEMENT_ARRAY_BUFFER, sizeof(indices), indices, GL_STATIC_DRAW);
glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 8 * sizeof(GLfloat), (GLvoid*)0);
glEnableVertexAttribArray(0);
glVertexAttribPointer(1, 3, GL_FLOAT, GL_FALSE, 8 * sizeof(GLfloat), (GLvoid*)(3 * sizeof(GLfloat)));
glEnableVertexAttribArray(1);
glVertexAttribPointer(2, 2, GL_FLOAT, GL_FALSE, 8 * sizeof(GLfloat), (GLvoid*)(6 * sizeof(GLfloat)));
glEnableVertexAttribArray(2);
int picWidth, picHeight;
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
unsigned char* image = SOIL_load_image("Texture/wallpaper.jpg", &picWidth, &picHeight, 0, SOIL_LOAD_RGB);
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, picWidth, picHeight, 0, GL_RGB, GL_UNSIGNED_BYTE, image);
glGenerateMipmap(GL_TEXTURE_2D);
SOIL_free_image_data(image);
glBindTexture(GL_TEXTURE_2D, 0);
glBindBuffer(GL_ARRAY_BUFFER, 0);
glBindVertexArray(0);
GLint transformLoc = glGetUniformLocation(shaderYellow.Program, "transform");
while (!glfwWindowShouldClose(window))
{
glfwPollEvents();
glClearColor(0.2f, 0.3f, 0.3f, 1.0f);
glClear(GL_COLOR_BUFFER_BIT);
glBindTexture(GL_TEXTURE_2D, texture);
shaderYellow.Use();
glm::mat4 model = glm::mat4(1.0f);
glm::mat4 view = glm::mat4(1.0f);
glm::mat4 projection = glm::mat4(1.0f);
model = glm::rotate(model, glm::radians(-55.0f), glm::vec3(1.0f, 0.0f, 0.0f));
view = glm::translate(view, glm::vec3(0.0f, 0.0f, -3.0f));
projection = glm::perspective(glm::radians(45.0f), (GLfloat)WIDTH / (GLfloat)HEIGHT, 0.1f, 100.0f);
GLint modelLoc = glGetUniformLocation(shaderYellow.Program, "model");
GLint viewLoc = glGetUniformLocation(shaderYellow.Program, "view");
GLint projLoc = glGetUniformLocation(shaderYellow.Program, "projection");
glUniformMatrix4fv(modelLoc, 1, GL_FALSE, glm::value_ptr(model));
glUniformMatrix4fv(viewLoc, 1, GL_FALSE, glm::value_ptr(view));
glUniformMatrix4fv(projLoc, 1, GL_FALSE, glm::value_ptr(projection));
glBindVertexArray(VAO);
glDrawElements(GL_TRIANGLES, 6, GL_UNSIGNED_INT, 0);
glBindVertexArray(0);
glfwSwapBuffers(window);
}
glDeleteVertexArrays(1, &VAO);
glDeleteBuffers(1, &VBO);
glDeleteBuffers(1, &EBO);
glfwTerminate();
return 0;
}
void key_callback(GLFWwindow* window, int key, int scancode, int action, int mode)
{
if (key == GLFW_KEY_ESCAPE && action == GLFW_PRESS)
glfwSetWindowShouldClose(window, GL_TRUE);
}
也可以通过各种调整矩阵来看下不同的效果
