对于室外3D 场景，通常可以通过在地平线上创造一些逼真的效果，来增强其真实感。
当我们极目远眺，目光越过附近的建筑和森林，我们习惯于看到远处的大型物体，例如：
云、群山或太阳（或夜空中的星星和月亮）。但是，将这些对象作为单个模型添加到场景中
可能会产生高到无法承受的性能成本。天空盒或天空穹顶提供了有效且相对简单的方法，
用来生成令人信服的地平线景观。
构建天空盒的另一种方法是使用OpenGL 纹理立方体贴图。OpenGL 立方体贴图比我们
在上一节中看到的简单方法稍微复杂一点。但是，使用OpenGL 立方体贴图有自己的优点，
例如减少接缝以及支持环境贴图。
OpenGL 纹理立方体贴图类似于稍后将要研究的3D 纹理，它们都使用3 个纹理坐标访
问——通常标记为（s, t, r）——而不是我们目前为止用到的两个。OpenGL 纹理立方体贴图
的另一个特性是，其中的图像以纹理图像的左上角（而不是通常的左下角）作为纹理坐标
（0, 0, 0），这通常是混乱产生的源头。
程序9.1 中展示的方法通过读入单个图像来为立方体贴图添加纹理，而程序9.2 中展示
的loadCubeMap()函数则读入6 个单独的立方体面图像文件。正如我们在第5 章中所学的，
有许多方法可以读取纹理图像，我们选择使用SOIL2 库。在这里，SOIL2 用于实例化和加
载OpenGL 立方体贴图也非常方便。我们先找到需要读入的文件， 然后调用
SOIL_load_OGL_cubemap()，其参数包括6 个图像文件和一些其他参数，类似于我们在第5
章中看到的SOIL_load_OGL_texture()。在使用OpenGL 立方体贴图时，无须垂直翻转纹理，
OpenGL 会自动进行处理，注意，loadCubeMap()函数放在“Utils.cpp”文件中。
init()函数现在包含一个函数调用以启用GL_TEXTURE_CUBE_MAP_SEAMLESS，它告
诉OpenGL 尝试混合立方体相邻的边以减少或消除接缝。在display()中，立方体的顶点像以
前一样沿管线向下发送，但这次不需要发送立方体的纹理坐标。我们将会看到，OpenGL 纹
理立方体贴图通常使用立方体的顶点位置作为其纹理坐标。之后禁用深度测试并绘制立方
体。然后为场景的其余部分重新启用深度测试。
完成后的OpenGL 纹理立方体贴图使用了int 类型的标识符进行引用。与阴影贴图时一
样，通过将纹理包裹模式设置为“夹紧到边缘”，可以减少沿边框的伪影。在这种情况下，
它还可以帮助进一步缩小接缝。请注意，这里需要为3 个纹理坐标s、t 和r 都设置纹理包
裹模式。
在片段着色器中使用名为samplerCube 的特殊类型的采样器访问纹理。在纹理立方体贴
图中，从采样器返回的值是沿着方向向量(s, t, r)从原点“看到”的纹素。因此，我们通常可
以简单地使用传入的插值顶点位置作为纹理坐标。在顶点着色器中，我们将立方体顶点位
置分配到输出纹理坐标属性中，以便在它们到达片段着色器时进行插值。另外需要注意，
在顶点着色器中，我们将传入的视图矩阵转换为3×3，然后再转换回4×4。这个“技巧”
有效地移除了平移分量，同时保留了旋转（回想一下，平移值在转换矩阵的第四列中）。这
样，就将立方体贴图固定在了摄像机位置，同时仍允许合成相机“环顾四周”。
#include "glew/glew.h"
#include "glfw/glfw3.h"
#include "glm/glm.hpp"
#include "glm/gtc/matrix_transform.hpp"
#include "glm/gtc/type_ptr.hpp"
#include "camera.h"
#include "Utils.h"
#include "Torus.h"
#include <iostream>
#include <fstream>
#include <string>
using namespace std;
static const float pai = 3.1415926f;
float toRadians(float degrees) { return degrees * 2.f * pai / (float)360.f; }
static const int screenWidth = 1920;
static const int screenHeight = 1080;
float cameraX = 0.f, cameraY = 0.f, cameraZ = 0.f;
float torLocX = 0.f, torLocY = 0.f, torLocZ = 0.f;
GLuint renderingProgram = 0, renderingProgramCubeMap = 0;
static const int numVAOs = 1;
static const int numVBOs = 5;
GLuint vao[numVAOs] = { 0 };
GLuint vbo[numVBOs] = { 0 };
GLuint brickTexture = 0, skyboxTexture = 0;
float rotAmt = 0.f;
// variable allocation for display
GLuint vLoc = 0, mvLoc = 0, projLoc = 0;
int width = 0, height = 0;
float aspect = 0.f;
glm::mat4 mMat(1.f), vMat(1.f), pMat(1.f), mvMat(1.f);
Torus myTorus(0.8f, 0.2f, 48);
int numTorusVertices = 0, numTorusIndices = 0;
Camera camera(glm::vec3(0.f, 0.f, 5.f));
GLboolean keys[1024] = { GL_FALSE };
GLboolean b_firstMouse = GL_TRUE;
float deltaTime = 0.f;
float lastFrame = 0.f;
float lastLocX = 0.f;
float lastLocY = 0.f;
void do_movement()
{
if (keys[GLFW_KEY_W])
{
camera.ProcessKeyboard(FORWARD, deltaTime);
}
if (keys[GLFW_KEY_S])
{
camera.ProcessKeyboard(BACKWARD, deltaTime);
}
if (keys[GLFW_KEY_A])
{
camera.ProcessKeyboard(LEFT, deltaTime);
}
if (keys[GLFW_KEY_D])
{
camera.ProcessKeyboard(RIGHT, deltaTime);
}
/*if (keys[GLFW_KEY_ESCAPE])
{
glfwSetWindowShouldClose(window, GL_TRUE);
}*/
}
void key_press_callback(GLFWwindow* window, int key, int scancode, int action, int mode)
{
if ((key == GLFW_KEY_ESCAPE) && (action == GLFW_PRESS))
{
glfwSetWindowShouldClose(window, GL_TRUE);
}
if (action == GLFW_PRESS)
{
keys[key] = GLFW_TRUE; //这里一定一定不能写成“==“，否则 按键WSAD按键失效！！！！！！！
}
else if (action == GLFW_RELEASE)
{
keys[key] = GLFW_FALSE; //这里一定一定不能写成“==“，否则 按键WSAD按键失效！！！！！！！
}
}
void mouse_move_callback(GLFWwindow* window, double xPos, double yPos)
{
if (b_firstMouse)
{
lastLocX = xPos;
lastLocY = yPos;
b_firstMouse = GL_FALSE;
}
float xOffset = xPos - lastLocX;
float yOffset = lastLocY - yPos;
lastLocX = xPos;
lastLocY = yPos;
camera.ProcessMouseMovement(xOffset, yOffset);
}
void mouse_scroll_callback(GLFWwindow* window, double xPos, double yPos)
{
camera.ProcessMouseScroll(yPos);
}
void setupVertices(void)
{
float cubeVertexPositions[108] =
{
-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, 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, -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, -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, 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, -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, 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, 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, 1.0f, -1.0f, 1.0f, -1.0f
};
numTorusVertices = myTorus.getNumVertices();
numTorusIndices = myTorus.getNumIndices();
vector<int> ind = myTorus.getIndices();
vector<glm::vec3> vert = myTorus.getVertices();
vector<glm::vec2> text = myTorus.getTexCoords();
vector<glm::vec3> norm = myTorus.getNormals();
vector<float> pValues;
vector<float> tValues;
vector<float> nValues;
for (int i=0; i<numTorusVertices; i++)
{
pValues.push_back(vert[i].x);
pValues.push_back(vert[i].y);
pValues.push_back(vert[i].z);
tValues.push_back(text[i].s);
tValues.push_back(text[i].t);
nValues.push_back(norm[i].x);
nValues.push_back(norm[i].y);
nValues.push_back(norm[i].z);
}
glGenVertexArrays(numVAOs, vao);
glBindVertexArray(vao[0]);
glGenBuffers(numVBOs, vbo);
glBindBuffer(GL_ARRAY_BUFFER, vbo[0]);
glBufferData(GL_ARRAY_BUFFER, sizeof(cubeVertexPositions), cubeVertexPositions, GL_STATIC_DRAW);
glBindBuffer(GL_ARRAY_BUFFER, vbo[1]);
glBufferData(GL_ARRAY_BUFFER, pValues.size() * sizeof(float), &pValues[0], GL_STATIC_DRAW);
glBindBuffer(GL_ARRAY_BUFFER, vbo[2]);
glBufferData(GL_ARRAY_BUFFER, tValues.size() * sizeof(float), &tValues[0], GL_STATIC_DRAW);
glBindBuffer(GL_ARRAY_BUFFER, vbo[3]);
glBufferData(GL_ARRAY_BUFFER, nValues.size() * sizeof(float), &nValues[0], GL_STATIC_DRAW);
glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, vbo[4]);
glBufferData(GL_ELEMENT_ARRAY_BUFFER, ind.size() * sizeof(int), &ind[0], GL_STATIC_DRAW);
}
void init(GLFWwindow* window)
{
renderingProgram = Utils::createShaderProgram("vertShader.vert", "fragShader.frag");
renderingProgramCubeMap = Utils::createShaderProgram("vertCubeShader.vert", "fragCubeShader.frag");
glfwGetFramebufferSize(window, &width, &height);
aspect = (float)width / (float)height;
pMat = glm::perspective(toRadians(45.f), aspect, 0.01f, 1000.f);
setupVertices();
brickTexture = Utils::loadTexture("brick1.jpg");
skyboxTexture = Utils::loadCubeMap("cubeMap"); // expects a folder name
//开启GL_TEXTURE_CUBE_MAP_SEAMLESS在天空盒子的边缘将对两个交界面进行采样混合，否则边缘将采用单边像素，会出现明显的裂缝。
glEnable(GL_TEXTURE_CUBE_MAP_SEAMLESS);
torLocX = 0.f, torLocY = 0.f, torLocZ = 0.f;
cameraX = 0.f, cameraY = 0.f, cameraZ = 5.f;
}
void display(GLFWwindow* window, double currentTime)
{
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
glClearColor(0.f, 0.5f, 1.f, 1.f);
//vMat = glm::translate(glm::mat4(1.f), glm::vec3(cameraX, cameraY, cameraZ));
// draw cube map
glUseProgram(renderingProgramCubeMap);
deltaTime = currentTime - lastFrame;
lastFrame = currentTime;
do_movement();
//这句必须要有，否则鼠标中键失效
pMat = glm::perspective(camera.Zoom, aspect, 0.01f, 1000.f);
vMat = camera.GetViewMatrix();
//没有这句，背景就没在相机视点上了,把圆环移到相机的位置
mMat = glm::translate(glm::mat4(1.f), glm::vec3(cameraX, cameraY, 4.f));
mvLoc = glGetUniformLocation(renderingProgramCubeMap, "mv_matrix");
glUniformMatrix4fv(vLoc, 1, GL_FALSE, glm::value_ptr(mvMat));
projLoc = glGetUniformLocation(renderingProgramCubeMap, "proj_matrix");
glUniformMatrix4fv(projLoc, 1, GL_FALSE, glm::value_ptr(pMat));
glBindBuffer(GL_ARRAY_BUFFER, vbo[0]);
glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 0, 0);
glEnableVertexAttribArray(0);
glActiveTexture(GL_TEXTURE0);
glBindTexture(GL_TEXTURE_CUBE_MAP, skyboxTexture);
//开启剔除操作效果
glEnable(GL_CULL_FACE);
//GL_CCW 表示窗口坐标上投影多边形的顶点顺序为逆时针方向的表面为正面。
//GL_CW 表示窗口坐标上投影多边形的顶点顺序为顺时针方向的表面为正面。
glFrontFace(GL_CCW);
glDisable(GL_DEPTH_TEST);
glDrawArrays(GL_TRIANGLES, 0, 36);
glEnable(GL_DEPTH_TEST);
// draw scene (in this case it is just a torus)
glUseProgram(renderingProgram);
mvLoc = glGetUniformLocation(renderingProgram, "mv_matrix");
projLoc = glGetUniformLocation(renderingProgram, "proj_matrix");
mMat = glm::translate(glm::mat4(1.f), glm::vec3(torLocX, torLocY, torLocZ));
mMat = glm::rotate(mMat, toRadians(35.f), glm::vec3(1.f, 0.f, 0.f));
mvMat = vMat * mMat;
glUniformMatrix4fv(mvLoc, 1, GL_FALSE, glm::value_ptr(mvMat));
glUniformMatrix4fv(projLoc, 1, GL_FALSE, glm::value_ptr(pMat));
//vbo[0] 是立方体纹理贴图
glBindBuffer(GL_ARRAY_BUFFER, vbo[1]);
glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 0, 0);
glEnableVertexAttribArray(0);
glBindBuffer(GL_ARRAY_BUFFER, vbo[2]);
glVertexAttribPointer(1, 2, GL_FLOAT, GL_FALSE, 0, 0);
glEnableVertexAttribArray(1);
glBindBuffer(GL_ARRAY_BUFFER, vbo[3]);
glVertexAttribPointer(2, 3, GL_FLOAT, GL_FALSE, 0, 0);
glEnableVertexAttribArray(2);
glBindBuffer(GL_ARRAY_BUFFER, vbo[4]);
glVertexAttribPointer(3, 3, GL_FLOAT, GL_FALSE, 0, 0);
glEnableVertexAttribArray(3);
glActiveTexture(GL_TEXTURE0);
glBindTexture(GL_TEXTURE_2D, brickTexture);
glClear(GL_DEPTH_BUFFER_BIT);
glEnable(GL_CULL_FACE);
glFrontFace(GL_CCW);
glDisable(GL_LEQUAL);
glDrawArrays(GL_TRIANGLES, 0, 36);
glEnable(GL_DEPTH_TEST);
glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, vbo[4]);
glDrawElements(GL_TRIANGLES, numTorusIndices, GL_UNSIGNED_INT, 0);
}
void window_size_callback(GLFWwindow* window, int newWidth, int newHeight)
{
aspect = (float)newWidth / (float)newHeight;
glViewport(0, 0, newWidth, newHeight);
pMat = glm::perspective(toRadians(45.f), aspect, 0.01f, 1000.f);
}
int main(int argc, char** argv)
{
int glfwState = glfwInit();
if (GLFW_FALSE == glfwState)
{
cout << "GLFW initialize failed,invoke glfwInit()......Error file:" << __FILE__ << "......Error line:" << __LINE__ << endl;
glfwTerminate();
exit(EXIT_FAILURE);
}
glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 4);
glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 6);
glfwWindowHint(GLFW_OPENGL_CORE_PROFILE, GLFW_OPENGL_PROFILE);
GLFWwindow* window = glfwCreateWindow(screenWidth, screenHeight, "skybox opengl six face", nullptr, nullptr);
if (!window)
{
cout << "GLFW create window failed,invoke glfwCreateWindow()......Error file:" << __FILE__ << "......Error line:" << __LINE__ << endl;
glfwTerminate();
exit(EXIT_FAILURE);
}
glfwMakeContextCurrent(window);
glfwSetWindowSizeCallback(window, window_size_callback);
//glfwSetKeyCallback(window)
int glewState = glewInit();
if (GLEW_OK != glewState)
{
cout << "GLEW initialize failed,invoke glewInit()......Error file:" << __FILE__ << "......Error line:" << __LINE__ << endl;
glfwTerminate();
exit(EXIT_FAILURE);
}
glfwSetWindowSizeCallback(window, window_size_callback);
glfwSetCursorPosCallback(window, mouse_move_callback);
glfwSetScrollCallback(window, mouse_scroll_callback);
glfwSetKeyCallback(window, key_press_callback);
init(window);
while (!glfwWindowShouldClose(window))
{
display(window, glfwGetTime());
glfwSwapBuffers(window);
glfwPollEvents();
}
glfwDestroyWindow(window);
glfwTerminate();
exit(EXIT_SUCCESS);
return 0;
}
1.顶点着色器
#version 460 core
layout(location = 0) in vec3 position;
layout(location = 1) in vec2 texCoord;
out vec2 tc;
uniform mat4 mv_matrix;
uniform mat4 proj_matrix;
layout(binding = 0) uniform sampler2D samp;
void main(void)
{
tc = texCoord;
gl_Position = proj_matrix * mv_matrix * vec4(position, 1.f);
}
2.片元着色器
#version 460 core
in vec2 tc;
out vec4 fragColor;
uniform mat4 mv_matrix;
uniform mat4 proj_matrix;
layout(binding = 0) uniform sampler2D samp;
void main(void)
{
fragColor = texture(samp, tc);
}
#version 460 core
layout(location = 0) in vec3 position;
layout(location = 1) in vec2 texCoord;
out vec3 tc;
uniform mat4 mv_matrix;
uniform mat4 proj_matrix;
layout(binding = 0) uniform sampler2D samp;
void main(void)
{
tc = position;
mat4 v3_matrix = mat4(mat3(mv_matrix));
gl_Position = proj_matrix * v3_matrix * vec4(position, 1.f);
}
4.立方体片元着色器
#version 460 core
in vec3 tc;
out vec4 fragColor;
uniform mat4 mv_matrix;
uniform mat4 proj_matrix;
layout(binding = 0) uniform samplerCube samp;
void main(void)
{
fragColor = texture(samp, tc);
}
layout(location = 0) in vec3 position;
layout(location = 1) in vec2 texCoord;
其中 location = 0，一定要和程序的顶点缓冲区vbo索引一致，否则渲染会出问题
如果写成这样：
运行结果
或者写成这样
中间圆环的纹理都会出问题
计算机图形学编程 使用OpenGL和C++