image.gif
image.png
代码：
#include "GLTools.h"
#include "GLShaderManager.h"
#include "GLFrustum.h"
#include "GLBatch.h"
#include "GLMatrixStack.h"
#include "GLGeometryTransform.h"
#include "StopWatch.h"
#include <math.h>
#include <stdio.h>
#ifdef __APPLE__
#include <glut/glut.h>
#else
#define FREEGLUT_STATIC
#include <GL/glut.h>
#endif
GLShaderManager shaderManager; // 着色器管理器
GLMatrixStack modelViewMatrix; // 模型视图矩阵堆栈
GLMatrixStack projectionMatrix; // 投影矩阵堆栈
GLFrustum viewFrustum; // 视景体
GLGeometryTransform transformPipeline; // 几何图形变换管道
GLTriangleBatch torusBatch; //大球
GLTriangleBatch sphereBatch; //小球
GLBatch floorBatch; //地板
//角色帧 照相机角色帧
GLFrame cameraFrame;
GLFrame objectFrame;
//**4、添加附加随机球
#define NUM_SPHERES 50
GLFrame spheres[NUM_SPHERES];
void SetupRC()
{
//1. 初始化
glClearColor(0, 0, 0, 1);
shaderManager.InitializeStockShaders();
glEnable(GL_DEPTH_TEST);
//3. 地板数据(物体坐标系)
floorBatch.Begin(GL_LINES, 324);
for(GLfloat x = -20.0; x <= 20.0f; x+= 0.5) {
floorBatch.Vertex3f(x, -0.55f, 20.0f);
floorBatch.Vertex3f(x, -0.55f, -20.0f);
floorBatch.Vertex3f(20.0f, -0.55f, x);
floorBatch.Vertex3f(-20.0f, -0.55f, x);
}
floorBatch.End();
//4. 设置一个球体(基于gltools模型)
gltMakeSphere(torusBatch, 0.4f, 40, 80);
//5. 绘制小球;
gltMakeSphere(sphereBatch, 0.1f, 13, 26);
//6. 随机位置放置小球球
for (int i = 0; i < NUM_SPHERES; i++) {
//y轴不变，X,Z产生随机值
GLfloat x = ((GLfloat)((rand() % 400) - 200 ) * 0.1f);
GLfloat z = ((GLfloat)((rand() % 400) - 200 ) * 0.1f);
//在y方向，将球体设置为0.0的位置，这使得它们看起来是飘浮在眼睛的高度
//对spheres数组中的每一个顶点，设置顶点数据
spheres[i].SetOrigin(x, 0.0f, z);
}
}
//进行调用以绘制场景
void RenderScene(void)
{
//3.
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
//1. 颜色(地板,大球颜色,小球颜色)
static GLfloat vFloorColor[] = {0.0f,1.0f,0.0f,1.0f};
static GLfloat vTorusColor[] = {1.0f,0.0f,0.0f,1.0f};
static GLfloat vSpereColor[] = {0.0f,0.0f,1.0f,1.0f};
//2. 动画
static CStopWatch rotTimer;
float yRot = rotTimer.GetElapsedSeconds()*60.0f;
modelViewMatrix.PushMatrix();
M3DMatrix44f mCamera;
cameraFrame.GetCameraMatrix(mCamera);
modelViewMatrix.PushMatrix(mCamera);
//4.地面绘制;
shaderManager.UseStockShader(GLT_SHADER_FLAT,transformPipeline.GetModelViewProjectionMatrix(),vFloorColor);
floorBatch.Draw();
//5. 设置点光源位置
M3DVector4f vLightPos = {0,10,5,1};
//6. 使得整个大球往里平移3.0
modelViewMatrix.Translate(0.0f, 0.0f, -3.0f);
//7. 大球
modelViewMatrix.PushMatrix();
modelViewMatrix.Rotate(yRot, 0, 1, 0);
shaderManager.UseStockShader(GLT_SHADER_POINT_LIGHT_DIFF,transformPipeline.GetModelViewMatrix(),transformPipeline.GetProjectionMatrix(),vLightPos,vTorusColor);
torusBatch.Draw();
modelViewMatrix.PopMatrix();
//8. 小球
for (int i = 0; i < NUM_SPHERES; i++) {
modelViewMatrix.PushMatrix();
modelViewMatrix.MultMatrix(spheres[i]);
shaderManager.UseStockShader(GLT_SHADER_POINT_LIGHT_DIFF,transformPipeline.GetModelViewMatrix(),transformPipeline.GetProjectionMatrix(),vLightPos,vSpereColor);
sphereBatch.Draw();
modelViewMatrix.PopMatrix();
}
//9.让一个小球围着大球公转;
modelViewMatrix.Rotate(yRot * -2.0f, 0, 1, 0);
modelViewMatrix.Translate(0.8f, 0.0f, 0.0f);
shaderManager.UseStockShader(GLT_SHADER_POINT_LIGHT_DIFF,transformPipeline.GetModelViewMatrix(),transformPipeline.GetProjectionMatrix(),vLightPos,vSpereColor);
sphereBatch.Draw();
modelViewMatrix.PopMatrix();
modelViewMatrix.PopMatrix();
glutSwapBuffers();
glutPostRedisplay();
}
//屏幕更改大小或已初始化
void ChangeSize(int nWidth, int nHeight)
{
//1. 设置视口
glViewport(0, 0, nWidth, nHeight);
//2. 创建投影矩阵
viewFrustum.SetPerspective(35.0f, float(nWidth)/float(nHeight), 1.0f, 100.0f);
projectionMatrix.LoadMatrix(viewFrustum.GetProjectionMatrix());
//3. 变换管道设置2个矩阵堆栈(管理)
transformPipeline.SetMatrixStacks(modelViewMatrix, projectionMatrix);
}
void SpeacialKeys(int key,int x,int y){
float linear = 0.1f;
float angular = float(m3dDegToRad(5.0f));
if (key == GLUT_KEY_UP) {
cameraFrame.MoveForward(linear);
}
if (key == GLUT_KEY_DOWN) {
cameraFrame.MoveForward(-linear);
}
if (key == GLUT_KEY_LEFT) {
cameraFrame.RotateWorld(angular, 0, 1, 0);
}
if (key == GLUT_KEY_RIGHT) {
cameraFrame.RotateWorld(-angular, 0, 1, 0);
}
}
int main(int argc, char* argv[])
{
gltSetWorkingDirectory(argv[0]);
glutInit(&argc, argv);
glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGB | GLUT_DEPTH);
glutInitWindowSize(800,600);
glutCreateWindow("OpenGL SphereWorld");
glutReshapeFunc(ChangeSize);
glutDisplayFunc(RenderScene);
glutSpecialFunc(SpeacialKeys);
GLenum err = glewInit();
if (GLEW_OK != err) {
fprintf(stderr, "GLEW Error: %s\n", glewGetErrorString(err));
return 1;
}
SetupRC();
glutMainLoop();
return 0;
}
这个公转代码你可能会有些疑问，还记得我在之前的基础变换的文章里讲过吗，平移和旋转以及缩放顺序不同效果是不一样的。
modelViewMatrix.Rotate(yRot * -2.0f, 0, 1, 0);
modelViewMatrix.Translate(0.8f, 0.0f, 0.0f);
你可能还是不理解，那么我再针对代码来分析一下
首先旋转的并不是小球，而是模型视图矩阵modelViewMatrix，移动的也是整个modelViewMatrix，小球只是绘制在当前模型视图矩阵堆栈中
造成该现象的原因是调用矩阵变换函数，会令局部坐标系也跟着平移和旋转，而不仅仅只是平移和旋转物体，平移和旋转针对的都是局部坐标系的操作。从矩阵变换的角度去考虑这个问题就是两个矩阵交换位置相乘结果不一样
那么为什么只有一个小球在公转呢？
这时候我们在想想push的作用，因为其他小球绘制前都进行了压栈，绘制完之后就出栈了，所以当前的矩阵变换根本不会影响到其他小球，这样你是不是对压栈又有了更深刻的理解。
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