【OpenGL】管理管线GLGeometryTransform和矩阵堆栈GLMatrixStack使用实例

目录

简单案例 

加点调料

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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;
}