目录
简单案例
主要看ChangeSize和RenderScene代码部分,模型视图矩阵堆栈会先进行PushMatrix拷贝顶部并放入顶部(单位矩阵),然后进行Translate和Rotate变换更新顶部矩阵,最后渲染后,PopMatrix出栈恢复。
定义了modelViewMatrix和projectionMatrix分别是模型视图矩阵堆栈和投影矩阵堆栈,并在ChangeSize时初始化投影矩阵和将投影矩阵放入LoadMatrix进入了projectionMatrix投影矩阵堆栈里,并将模型视图矩阵堆栈和投影矩阵堆栈放入transformPipeline几何变换管线对象 进行管理。注意:没有进行任何LoadMatrix操作的模型视图矩阵堆栈默认顶部就有一个单位矩阵的,即矩阵堆栈对象默认就有一个单位矩阵!
虽然这些操作看起来都可以使用原本之前介绍的m3dMatrixMultiply来进行相乘矩阵来得到模型视图投影矩阵,但却有一个操作是节省了,那就是不需要每一次渲染时重载单位矩阵!但更大的用途在添加摄像机时,这个管理管线就非常有用。其中transformPipeline.GetModelViewProjectionMatrix() 会将管理器中的模型视图矩阵堆栈的顶部矩阵元素 和 投影矩阵堆栈的顶部矩阵元素 相乘得到 模型视图投影矩阵返回,传给UseStockShader使用,最后别忘了将模型视图矩阵堆栈的顶部元素PopMatrix(),不然下一次渲染拷贝的就不是单位矩阵了!
最初的代码只有固定的几何图形(底板)和一个变换(旋转)的对象。
// SphereWorld.cpp
// OpenGL SuperBible
// New and improved (performance) sphere world
// Program by Richard S. Wright Jr.
#pragma comment(lib, "gltools.lib")
#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; // Shader Manager
GLMatrixStack modelViewMatrix; // Modelview Matrix
GLMatrixStack projectionMatrix; // Projection Matrix
GLFrustum viewFrustum; // View Frustum
GLGeometryTransform transformPipeline; // Geometry Transform Pipeline
GLTriangleBatch torusBatch;
GLBatch floorBatch;
//
// This function does any needed initialization on the rendering
// context.
void SetupRC()
{
// Initialze Shader Manager
shaderManager.InitializeStockShaders();
glEnable(GL_DEPTH_TEST);
glPolygonMode(GL_FRONT_AND_BACK, GL_LINE);
glClearColor(0.0f, 0.0f, 0.0f, 1.0f);
// This makes a torus
gltMakeTorus(torusBatch, 0.4f, 0.15f, 30, 30);
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();
}
///
// Screen changes size or is initialized
void ChangeSize(int nWidth, int nHeight)
{
glViewport(0, 0, nWidth, nHeight);
// Create the projection matrix, and load it on the projection matrix stack
viewFrustum.SetPerspective(35.0f, float(nWidth) / float(nHeight), 1.0f, 100.0f);
projectionMatrix.LoadMatrix(viewFrustum.GetProjectionMatrix());
// Set the transformation pipeline to use the two matrix stacks
transformPipeline.SetMatrixStacks(modelViewMatrix, projectionMatrix);
}
// Called to draw scene
void RenderScene(void)
{
// Color values
static GLfloat vFloorColor[] = { 0.0f, 1.0f, 0.0f, 1.0f };
static GLfloat vTorusColor[] = { 1.0f, 0.0f, 0.0f, 1.0f };
// Time Based animation
static CStopWatch rotTimer;
float yRot = rotTimer.GetElapsedSeconds() * 60.0f;
// Clear the color and depth buffers
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
// Save the current modelview matrix (the identity matrix)
modelViewMatrix.PushMatrix();
// Draw the ground
shaderManager.UseStockShader(GLT_SHADER_FLAT,
transformPipeline.GetModelViewProjectionMatrix(),
vFloorColor);
floorBatch.Draw();
// Draw the spinning Torus
modelViewMatrix.Translate(0.0f, 0.0f, -2.5f);
modelViewMatrix.Rotate(yRot, 0.0f, 1.0f, 0.0f);
shaderManager.UseStockShader(GLT_SHADER_FLAT, transformPipeline.GetModelViewProjectionMatrix(),
vTorusColor);
torusBatch.Draw();
// Restore the previous modleview matrix (the idenity matrix)
modelViewMatrix.PopMatrix();
// Do the buffer Swap
glutSwapBuffers();
// Tell GLUT to do it again
glutPostRedisplay();
}
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);
GLenum err = glewInit();
if (GLEW_OK != err) {
fprintf(stderr, "GLEW Error: %s\n", glewGetErrorString(err));
return 1;
}
SetupRC();
glutMainLoop();
return 0;
}
加点调料
主要看RenderScene,注意看PushMatrix的时机变成了在平移模型视图矩阵堆栈之后进行,即保存了平移后的矩阵内容,拷贝出了一个新的平移后矩阵内容 进行花托旋转,花托绘制完成后,进行PopMatrix恢复到第一步做的平移,接着进行新的旋转和平移,影响后面渲染的球体,球体渲染后,PopMatrix恢复为单位矩阵。这里主要一点是球体实际上发生了2次平移,第一次是绘制花托时的那个平移,第二次是球体绘制前的那个平移,而旋转只进行了球体那一次旋转,因为在绘制球体之前就进行了PopMatrix来清除花托的旋转矩阵。从这里可看出堆栈的用途了,但它真正的威力还未完全体现出来!
// SphereWorld.cpp
// OpenGL SuperBible
// New and improved (performance) sphere world
// Program by Richard S. Wright Jr.
#pragma comment(lib, "gltools.lib")
#include <GLTools.h>
#include <GLShaderManager.h>
#include <GLFrustum.h>
#include <GLBatch.h>
#include <GLFrame.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; // Shader Manager
GLMatrixStack modelViewMatrix; // Modelview Matrix
GLMatrixStack projectionMatrix; // Projection Matrix
GLFrustum viewFrustum; // View Frustum
GLGeometryTransform transformPipeline; // Geometry Transform Pipeline
GLTriangleBatch torusBatch;
GLBatch floorBatch;
GLTriangleBatch sphereBatch;
GLFrame cameraFrame;
//
// This function does any needed initialization on the rendering
// context.
void SetupRC()
{
// Initialze Shader Manager
shaderManager.InitializeStockShaders();
glEnable(GL_DEPTH_TEST);
glPolygonMode(GL_FRONT_AND_BACK, GL_LINE);
glClearColor(0.0f, 0.0f, 0.0f, 1.0f);
// This makes a torus
gltMakeTorus(torusBatch, 0.4f, 0.15f, 30, 30);
// This make a sphere
gltMakeSphere(sphereBatch, 0.1f, 26, 13);
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();
}
///
// Screen changes size or is initialized
void ChangeSize(int nWidth, int nHeight)
{
glViewport(0, 0, nWidth, nHeight);
// Create the projection matrix, and load it on the projection matrix stack
viewFrustum.SetPerspective(35.0f, float(nWidth) / float(nHeight), 1.0f, 100.0f);
projectionMatrix.LoadMatrix(viewFrustum.GetProjectionMatrix());
// Set the transformation pipeline to use the two matrix stacks
transformPipeline.SetMatrixStacks(modelViewMatrix, projectionMatrix);
}
// Respond to arrow keys by moving the camera frame of reference
void SpecialKeys(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, 0.0f, 1.0f, 0.0f);
if (key == GLUT_KEY_RIGHT)
cameraFrame.RotateWorld(-angular, 0.0f, 1.0f, 0.0f);
}
// Called to draw scene
void RenderScene(void)
{
// Color values
static GLfloat vFloorColor[] = { 0.0f, 1.0f, 0.0f, 1.0f };
static GLfloat vTorusColor[] = { 1.0f, 0.0f, 0.0f, 1.0f };
static GLfloat vSphereColor[] = { 0.0f, 0.0f, 1.0f, 1.0f };
// Time Based animation
static CStopWatch rotTimer;
float yRot = rotTimer.GetElapsedSeconds() * 60.0f;
// Clear the color and depth buffers
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
// Save the current modelview matrix (the identity matrix)
modelViewMatrix.PushMatrix();
M3DMatrix44f mCamera;
cameraFrame.GetCameraMatrix(mCamera);
modelViewMatrix.PushMatrix(mCamera);
// Draw the ground
shaderManager.UseStockShader(GLT_SHADER_FLAT,
transformPipeline.GetModelViewProjectionMatrix(),
vFloorColor);
floorBatch.Draw();
// Draw the spinning Torus
modelViewMatrix.Translate(0.0f, 0.0f, -2.5f);
// Save the Translation
modelViewMatrix.PushMatrix();
// Apply a rotation and draw the torus
modelViewMatrix.Rotate(yRot, 0.0f, 1.0f, 0.0f);
shaderManager.UseStockShader(GLT_SHADER_FLAT, transformPipeline.GetModelViewProjectionMatrix(),
vTorusColor);
torusBatch.Draw();
modelViewMatrix.PopMatrix(); // "Erase" the Rotation from before
// Apply another rotation, followed by a translation, then draw the sphere
modelViewMatrix.Rotate(yRot * -2.0f, 0.0f, 1.0f, 0.0f);
modelViewMatrix.Translate(0.8f, 0.0f, 0.0f);
shaderManager.UseStockShader(GLT_SHADER_FLAT, transformPipeline.GetModelViewProjectionMatrix(),
vSphereColor);
sphereBatch.Draw();
// Restore the previous modleview matrix (the identity matrix)
modelViewMatrix.PopMatrix();
modelViewMatrix.PopMatrix();
// Do the buffer Swap
glutSwapBuffers();
// Tell GLUT to do it again
glutPostRedisplay();
}
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");
glutSpecialFunc(SpecialKeys);
glutReshapeFunc(ChangeSize);
glutDisplayFunc(RenderScene);
GLenum err = glewInit();
if (GLEW_OK != err) {
fprintf(stderr, "GLEW Error: %s\n", glewGetErrorString(err));
return 1;
}
SetupRC();
glutMainLoop();
return 0;
}