现在我们扩展法线贴图的概念——从纹理图像用于扰动法向量到扰乱顶点位置本身。实
际上，以这种方式修改对象的几何体具有一定的优势，例如使表面特征沿着对象的边缘可
见，并使特征能够响应阴影贴图。我们将会看到，它还可以帮助构建地形。
一种实用的方法是使用纹理图像来存储高度值，然后使用该高度值来提升（或降低）顶
点位置。含有高度信息的图像称为高度图，使用高度图更改对象的顶点的方法称为高度贴
图①。高度图通常将高度信息编码为灰度颜色：（0,0,0）（黑色）=低高度，（1,1,1）（白色）=
高高度。这样一来通过算法或使用“画图”程序就可以轻松创建高度图。图像的对比度越
高，其表示的高度变化越大。这些概念将在图1（显示随机生成的地图）和图10.13（显
示有组织的模式的地图）中说明。
图1
改变顶点位置是否有用取决于改变的模型。顶点操作可以在顶点着色器中轻松完成，当模型顶点细节级别够高（例如在足够高精度的球体中）时，改变顶点高度的方法效果很好。但是，当模型的顶点数量很少（例如立方体的角）时，渲染对象的表面需要依赖于光栅器中的顶点插值来填充细节。当顶点着色器中可用于改变高度的顶点很少时，许多像素的高度将无法从高度图中检索，而需要由插值生成，从而导致表面细节较差。当然，在片段着色器中是不可能进行顶点操作的，因为这时顶点已被光栅化为像素位置。程序 展示了一个将顶点“向外”（即在表面法向量的方向上）移动的顶点着色器代
码。它通过将顶点法向量乘以从高度图检索所得的值，然后将该乘积与顶点位置相加，以
“向外”移动顶点。
#include <GL\glew.h>
#include <GLFW\glfw3.h>
#include <SOIL2\soil2.h>
#include <string>
#include <iostream>
#include <fstream>
#include <glm\gtc\type_ptr.hpp> // glm::value_ptr
#include <glm\gtc\matrix_transform.hpp> // glm::translate, glm::rotate, glm::scale, glm::perspective
#include "ImportedModel.h"
#include "Utils.h"
using namespace std;
float toRadians(float degrees) { return (degrees * 2.0f * 3.14159f) / 360.0f; }
#define numVAOs 1
#define numVBOs 3
float cameraX, cameraY, cameraZ;
float gndLocX, gndLocY, gndLocZ;
GLuint renderingProgram;
GLuint vao[numVAOs];
GLuint vbo[numVBOs];
// variable allocation for display
GLuint mvLoc, projLoc;
int width, height;
float aspect;
glm::mat4 pMat, vMat, mMat, mvMat;
ImportedModel ground("grid.obj");
int numGroundVertices;
GLuint heightMap;
GLuint heightTexture;
void setupVertices(void) {
numGroundVertices = ground.getNumVertices();
std::vector<glm::vec3> vert = ground.getVertices();
std::vector<glm::vec2> tex = ground.getTextureCoords();
std::vector<glm::vec3> norm = ground.getNormals();
std::vector<float> pvalues;
std::vector<float> tvalues;
std::vector<float> nvalues;
for (int i = 0; i < numGroundVertices; i++) {
pvalues.push_back((vert[i]).x);
pvalues.push_back((vert[i]).y);
pvalues.push_back((vert[i]).z);
tvalues.push_back((tex[i]).x);
tvalues.push_back((tex[i]).y);
nvalues.push_back((norm[i]).x);
nvalues.push_back((norm[i]).y);
nvalues.push_back((norm[i]).z);
}
glGenVertexArrays(1, vao);
glBindVertexArray(vao[0]);
glGenBuffers(numVBOs, vbo);
glBindBuffer(GL_ARRAY_BUFFER, vbo[0]);
glBufferData(GL_ARRAY_BUFFER, pvalues.size() * 4, &pvalues[0], GL_STATIC_DRAW);
glBindBuffer(GL_ARRAY_BUFFER, vbo[1]);
glBufferData(GL_ARRAY_BUFFER, tvalues.size() * 4, &tvalues[0], GL_STATIC_DRAW);
glBindBuffer(GL_ARRAY_BUFFER, vbo[2]);
glBufferData(GL_ARRAY_BUFFER, nvalues.size() * 4, &nvalues[0], GL_STATIC_DRAW);
}
void init(GLFWwindow* window) {
renderingProgram = Utils::createShaderProgram("vertShader.glsl", "fragShader.glsl");
cameraX = 0.03f; cameraY = 0.03f; cameraZ = 0.8f;
gndLocX = 0.0f; gndLocY = 0.0f; gndLocZ = 0.0f;
glfwGetFramebufferSize(window, &width, &height);
aspect = (float)width / (float)height;
pMat = glm::perspective(1.0472f, aspect, 0.1f, 1000.0f);
setupVertices();
heightTexture = Utils::loadTexture("heightTexture.jpg");
heightMap = Utils::loadTexture("height.jpg");
}
void display(GLFWwindow* window, double currentTime) {
glClear(GL_DEPTH_BUFFER_BIT);
glClearColor(0.0, 0.0, 0.0, 1.0);
glClear(GL_COLOR_BUFFER_BIT);
glUseProgram(renderingProgram);
mvLoc = glGetUniformLocation(renderingProgram, "mv_matrix");
projLoc = glGetUniformLocation(renderingProgram, "proj_matrix");
vMat = glm::translate(glm::mat4(1.0f), glm::vec3(-cameraX, -cameraY, -cameraZ));
mMat = glm::translate(glm::mat4(1.0f), glm::vec3(gndLocX, gndLocY, gndLocZ));
mMat = glm::rotate(mMat, toRadians(15.0f), glm::vec3(1.0f, 0.0f, 0.0f));
mvMat = vMat * mMat;
glUniformMatrix4fv(mvLoc, 1, GL_FALSE, glm::value_ptr(mvMat));
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);
glBindBuffer(GL_ARRAY_BUFFER, vbo[1]);
glVertexAttribPointer(1, 2, GL_FLOAT, GL_FALSE, 0, 0);
glEnableVertexAttribArray(1);
glBindBuffer(GL_ARRAY_BUFFER, vbo[2]);
glVertexAttribPointer(2, 3, GL_FLOAT, GL_FALSE, 0, 0);
glEnableVertexAttribArray(2);
glActiveTexture(GL_TEXTURE0);
glBindTexture(GL_TEXTURE_2D, heightTexture);
glActiveTexture(GL_TEXTURE1);
glBindTexture(GL_TEXTURE_2D, heightMap);
glEnable(GL_CULL_FACE);
glFrontFace(GL_CCW);
glEnable(GL_DEPTH_TEST);
glDepthFunc(GL_LEQUAL);
glDrawArrays(GL_TRIANGLES, 0, numGroundVertices);
}
void window_size_callback(GLFWwindow* win, int newWidth, int newHeight) {
aspect = (float)newWidth / (float)newHeight;
glViewport(0, 0, newWidth, newHeight);
pMat = glm::perspective(1.0472f, aspect, 0.1f, 1000.0f);
}
int main(void) {
if (!glfwInit()) { exit(EXIT_FAILURE); }
glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 4);
glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 3);
GLFWwindow* window = glfwCreateWindow(800, 800, "Chapter10 - program4a", NULL, NULL);
glfwMakeContextCurrent(window);
if (glewInit() != GLEW_OK) { exit(EXIT_FAILURE); }
glfwSwapInterval(1);
glfwSetWindowSizeCallback(window, window_size_callback);
init(window);
while (!glfwWindowShouldClose(window)) {
display(window, glfwGetTime());
glfwSwapBuffers(window);
glfwPollEvents();
}
glfwDestroyWindow(window);
glfwTerminate();
exit(EXIT_SUCCESS);
}
## 2.着色器程序
顶点着色器
```cpp
#version 430
layout (location=0) in vec3 vertPos;
layout (location=1) in vec2 texCoord;
layout (location=2) in vec3 vertNormal;
out vec2 tc;
uniform mat4 mv_matrix;
uniform mat4 proj_matrix;
layout (binding=0) uniform sampler2D t; // for texture
layout (binding=1) uniform sampler2D h; // for height map
void main(void)
{ vec4 p = vec4(vertPos,1.0) + vec4((vertNormal*((texture(h, texCoord).r)/5.0f)),1.0f);
tc = texCoord;
gl_Position = proj_matrix * mv_matrix * p;
}
2.片元着色器
#version 430
in vec2 tc;
out vec4 fragColor;
uniform mat4 mv_matrix;
uniform mat4 proj_matrix;
layout (binding=0) uniform sampler2D t; // for texture
layout (binding=1) uniform sampler2D h; // for height map
void main(void)
{ fragColor = texture(t, tc);
}
