【OpenGL】各向异性过滤案例

 

第一张图是GL_NEAREST没开启各向异性的，第二张图开启了各向异性变的比较不那么斑驳了，其他效果可自行测试。

// 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)
{
	GLfloat fLargest;
	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;

		case 6:
			glGetFloatv(GL_MAX_TEXTURE_MAX_ANISOTROPY_EXT, &fLargest);
			glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MAX_ANISOTROPY_EXT, fLargest);
			break;

		case 7:
			glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MAX_ANISOTROPY_EXT, 1.0f);
			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("Anisotropic 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);
	glutAddMenuEntry("Anisotropic Filter", 6);
	glutAddMenuEntry("Anisotropic Off", 7);

	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;
}