【OpenGL】活动的Mip贴图 Tunnel实例

其他 2021-04-05 14:55:02 阅读次数: 0

 GL_NEAREST ，可右键出现菜单选中不同的过滤方式观察

案例有3个纹理对象，分别渲染天花板、地面和墙体，在SetupRC函数有进行分配纹理对象3个，并进行循环3次执行不同纹理对象的捆绑到2D纹理状态且加载纹理设置过滤器和环绕模式，生成Mip贴图。注意：每一次循环进行的加载纹理和设置纹理参数都是应用于它对应的纹理对象，而纹理对象会捆绑到2D纹理状态。即一种纹理状态（2D纹理状态）对应了三个纹理对象，循环结束后是最后一个纹理对象捆绑2D纹理状态，即TEXTURE_CEILING标识的纹理对象。在之后进行批次Draw之前需要根据需要重新glBindTexture，来切换渲染使用的贴图。

在结束时需要glDeleteTextures(TEXTURE_COUNT, textures);来删除所有纹理对象。
可注意到为什么切换过滤模式的代码只有对GL_TEXTURE_MIN_FILTER 即缩小过滤器进行设置了过滤模式，因为没有针对Mip贴图的放大过滤处理，即当需要进行放大过滤处理时，此时肯定是已经使用最大Mip贴图但仍然需要放大处理，此时Mip贴图已经没有更大的Mip层提供进行GL_XXXX_MIPMAP_XXXX了，XXXX是指NEAREST或LINEAR，即在Mip层之间进行最邻近选择或线性插值拿到新的Mip贴图。

// Tunnel.cpp
// Demonstrates mipmapping and using texture objects
// OpenGL SuperBible
// 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>

#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

GLBatch             floorBatch;
GLBatch             ceilingBatch;
GLBatch             leftWallBatch;
GLBatch             rightWallBatch;

GLfloat             viewZ = -65.0f;

// Texture objects
#define TEXTURE_BRICK   0
#define TEXTURE_FLOOR   1
#define TEXTURE_CEILING 2
#define TEXTURE_COUNT   3
GLuint  textures[TEXTURE_COUNT];
const char *szTextureFiles[TEXTURE_COUNT] = { "brick.tga", "floor.tga", "ceiling.tga" };



///
// Change texture filter for each texture object
void ProcessMenu(int value)
{
	GLint iLoop;

	for (iLoop = 0; iLoop < TEXTURE_COUNT; iLoop++)
	{
		glBindTexture(GL_TEXTURE_2D, textures[iLoop]);

		switch (value)
		{
		case 0:
			glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
			break;

		case 1:
			glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
			break;

		case 2:
			glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST_MIPMAP_NEAREST);
			break;

		case 3:
			glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST_MIPMAP_LINEAR);
			break;

		case 4:
			glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR_MIPMAP_NEAREST);
			break;

		case 5:
			glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR_MIPMAP_LINEAR);
			break;
		}
	}

	// Trigger Redraw
	glutPostRedisplay();
}


//
// This function does any needed initialization on the rendering
// context.  Here it sets up and initializes the texture objects.
void SetupRC()
{
	GLbyte *pBytes;
	GLint iWidth, iHeight, iComponents;
	GLenum eFormat;
	GLint iLoop;

	// Black background
	glClearColor(0.0f, 0.0f, 0.0f, 1.0f);

	shaderManager.InitializeStockShaders();

	// Load textures
	glGenTextures(TEXTURE_COUNT, textures);
	for (iLoop = 0; iLoop < TEXTURE_COUNT; iLoop++)
	{
		// Bind to next texture object
		glBindTexture(GL_TEXTURE_2D, textures[iLoop]);

		// Load texture, set filter and wrap modes
		pBytes = gltReadTGABits(szTextureFiles[iLoop], &iWidth, &iHeight,
			&iComponents, &eFormat);

		// Load texture, set filter and wrap modes
		glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
		glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
		glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
		glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
		glTexImage2D(GL_TEXTURE_2D, 0, iComponents, iWidth, iHeight, 0, eFormat, GL_UNSIGNED_BYTE, pBytes);
		glGenerateMipmap(GL_TEXTURE_2D);
		// Don't need original texture data any more
		free(pBytes);
	}

	// Build Geometry
	GLfloat z;
	floorBatch.Begin(GL_TRIANGLE_STRIP, 28, 1);
	for (z = 60.0f; z >= 0.0f; z -= 10.0f)
	{
		floorBatch.MultiTexCoord2f(0, 0.0f, 0.0f);
		floorBatch.Vertex3f(-10.0f, -10.0f, z);

		floorBatch.MultiTexCoord2f(0, 1.0f, 0.0f);
		floorBatch.Vertex3f(10.0f, -10.0f, z);

		floorBatch.MultiTexCoord2f(0, 0.0f, 1.0f);
		floorBatch.Vertex3f(-10.0f, -10.0f, z - 10.0f);

		floorBatch.MultiTexCoord2f(0, 1.0f, 1.0f);
		floorBatch.Vertex3f(10.0f, -10.0f, z - 10.0f);
	}
	floorBatch.End();

	ceilingBatch.Begin(GL_TRIANGLE_STRIP, 28, 1);
	for (z = 60.0f; z >= 0.0f; z -= 10.0f)
	{
		ceilingBatch.MultiTexCoord2f(0, 0.0f, 1.0f);
		ceilingBatch.Vertex3f(-10.0f, 10.0f, z - 10.0f);

		ceilingBatch.MultiTexCoord2f(0, 1.0f, 1.0f);
		ceilingBatch.Vertex3f(10.0f, 10.0f, z - 10.0f);

		ceilingBatch.MultiTexCoord2f(0, 0.0f, 0.0f);
		ceilingBatch.Vertex3f(-10.0f, 10.0f, z);

		ceilingBatch.MultiTexCoord2f(0, 1.0f, 0.0f);
		ceilingBatch.Vertex3f(10.0f, 10.0f, z);
	}
	ceilingBatch.End();

	leftWallBatch.Begin(GL_TRIANGLE_STRIP, 28, 1);
	for (z = 60.0f; z >= 0.0f; z -= 10.0f)
	{
		leftWallBatch.MultiTexCoord2f(0, 0.0f, 0.0f);
		leftWallBatch.Vertex3f(-10.0f, -10.0f, z);

		leftWallBatch.MultiTexCoord2f(0, 0.0f, 1.0f);
		leftWallBatch.Vertex3f(-10.0f, 10.0f, z);

		leftWallBatch.MultiTexCoord2f(0, 1.0f, 0.0f);
		leftWallBatch.Vertex3f(-10.0f, -10.0f, z - 10.0f);

		leftWallBatch.MultiTexCoord2f(0, 1.0f, 1.0f);
		leftWallBatch.Vertex3f(-10.0f, 10.0f, z - 10.0f);
	}
	leftWallBatch.End();


	rightWallBatch.Begin(GL_TRIANGLE_STRIP, 28, 1);
	for (z = 60.0f; z >= 0.0f; z -= 10.0f)
	{
		rightWallBatch.MultiTexCoord2f(0, 0.0f, 0.0f);
		rightWallBatch.Vertex3f(10.0f, -10.0f, z);

		rightWallBatch.MultiTexCoord2f(0, 0.0f, 1.0f);
		rightWallBatch.Vertex3f(10.0f, 10.0f, z);

		rightWallBatch.MultiTexCoord2f(0, 1.0f, 0.0f);
		rightWallBatch.Vertex3f(10.0f, -10.0f, z - 10.0f);

		rightWallBatch.MultiTexCoord2f(0, 1.0f, 1.0f);
		rightWallBatch.Vertex3f(10.0f, 10.0f, z - 10.0f);
	}
	rightWallBatch.End();
}

///
// Shutdown the rendering context. Just deletes the
// texture objects
void ShutdownRC(void)
{
	glDeleteTextures(TEXTURE_COUNT, textures);
}


///
// Respond to arrow keys, move the viewpoint back
// and forth
void SpecialKeys(int key, int x, int y)
{
	if (key == GLUT_KEY_UP)
		viewZ += 0.5f;

	if (key == GLUT_KEY_DOWN)
		viewZ -= 0.5f;

	// Refresh the Window
	glutPostRedisplay();
}

/
// Change viewing volume and viewport.  Called when window is resized
void ChangeSize(int w, int h)
{
	GLfloat fAspect;

	// Prevent a divide by zero
	if (h == 0)
		h = 1;

	// Set Viewport to window dimensions
	glViewport(0, 0, w, h);

	fAspect = (GLfloat)w / (GLfloat)h;

	// Produce the perspective projection
	viewFrustum.SetPerspective(80.0f, fAspect, 1.0, 120.0);
	projectionMatrix.LoadMatrix(viewFrustum.GetProjectionMatrix());
	transformPipeline.SetMatrixStacks(modelViewMatrix, projectionMatrix);

}

///
// Called to draw scene
void RenderScene(void)
{
	// Clear the window with current clearing color
	glClear(GL_COLOR_BUFFER_BIT);

	modelViewMatrix.PushMatrix();
	modelViewMatrix.Translate(0.0f, 0.0f, viewZ);

	shaderManager.UseStockShader(GLT_SHADER_TEXTURE_REPLACE, transformPipeline.GetModelViewProjectionMatrix(), 0);

	glBindTexture(GL_TEXTURE_2D, textures[TEXTURE_FLOOR]);
	floorBatch.Draw();

	glBindTexture(GL_TEXTURE_2D, textures[TEXTURE_CEILING]);
	ceilingBatch.Draw();

	glBindTexture(GL_TEXTURE_2D, textures[TEXTURE_BRICK]);
	leftWallBatch.Draw();
	rightWallBatch.Draw();

	modelViewMatrix.PopMatrix();

	// Buffer swap
	glutSwapBuffers();
}


//
// Program entry point
int main(int argc, char *argv[])
{
	gltSetWorkingDirectory(argv[0]);

	// Standard initialization stuff
	glutInit(&argc, argv);
	glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGB);
	glutInitWindowSize(800, 600);
	glutCreateWindow("Tunnel");
	glutReshapeFunc(ChangeSize);
	glutSpecialFunc(SpecialKeys);
	glutDisplayFunc(RenderScene);

	// Add menu entries to change filter
	glutCreateMenu(ProcessMenu);
	glutAddMenuEntry("GL_NEAREST", 0);
	glutAddMenuEntry("GL_LINEAR", 1);
	glutAddMenuEntry("GL_NEAREST_MIPMAP_NEAREST", 2);
	glutAddMenuEntry("GL_NEAREST_MIPMAP_LINEAR", 3);
	glutAddMenuEntry("GL_LINEAR_MIPMAP_NEAREST", 4);
	glutAddMenuEntry("GL_LINEAR_MIPMAP_LINEAR", 5);

	glutAttachMenu(GLUT_RIGHT_BUTTON);

	GLenum err = glewInit();
	if (GLEW_OK != err) {
		fprintf(stderr, "GLEW Error: %s\n", glewGetErrorString(err));
		return 1;
	}


	// Startup, loop, shutdown
	SetupRC();
	glutMainLoop();
	ShutdownRC();

	return 0;
}

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