OpenGL藍寶書第五章5.4Tunnuel 紋理映射和過濾：較好的可讀性代碼

主要處理了紋理貼圖和頂點映射的關係。根據法線先確認環繞方向。然後根據繪製的primitive_type完成紋理頂點直接的映射。

哪裏來，哪裏回；根據法線來確認逆時針方向。strip的畫法要熟悉，從其實的兩個頂點開始已折線的形式前進

GL_TRIANGLES_STRIP是常用的繪製方式，在循環代碼中使用四個頂點+循環控制量能完成大量的幾何圖形繪製。這裏我犯了個錯誤，沒意識到折線的的前進方向問題，導致紋理映射出現了偏差，一度去懷疑modelViewMatrix的配置是否正確。但是我發現原書中的代碼沒有使用法線去控制貼圖頂點之前的關係，而是使用了相反的方向和對應的座標，我是看不懂了，還是踏實得配置法線接着再執行的映射。

//在三線性過濾的模式下開啓各項異性過濾就會發現計算很遠距離的仍然能看到磚縫

這個就是各項異性的優勢，但是使用普通的GL_LINEAR過濾就能有一個較好的視覺效果，雖然逼真度不是很高。

#include <GLTools.h>
#include <GLMatrixStack.h>
#include <GLFrame.h>
#include <GLFrustum.h>
#include <GLGeometryTransform.h>
#include <GLShaderManager.h>
#include <StopWatch.h>

#ifdef __APPLE__
#include <glut/glut.h>
#else
#define FREEGLUT_STATIC
#include <GL/glut.h>
#endif


GLFrame cameraFrame;
GLFrustum viewFrustum;
GLMatrixStack projctionMatrix;
GLMatrixStack mvpMatrix;
GLMatrixStack modelViewMatrix;
GLShaderManager shaderManager;
GLGeometryTransform transformPipeLine;


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

GLfloat viewZ = -65.0f;

#define TEXTURE_BRICK 0
#define TEXTURE_FLOOR 1
#define TEXTURE_CEILING 2
#define TEXTURE_COUNT 3

GLuint uiTextures[TEXTURE_COUNT];
const char * uiTextureName[TEXTURE_COUNT] = {"brick.tga","ceiling.tga","floor.tga"};

void ChangeSize(int w, int h)
{
	if (h <= 0)
	{
		h = 1;
	}

	glViewport(0, 0, w, h);
	viewFrustum.SetPerspective(80.0f, float(w) / float(h), 1.0f, 120.0f);
	projctionMatrix.LoadMatrix(viewFrustum.GetProjectionMatrix());
	transformPipeLine.SetMatrixStacks(modelViewMatrix, projctionMatrix);
}

void ProcessMenu(int value)
{
	GLfloat fLargest;
	for (size_t i = 0; i < TEXTURE_COUNT; ++i)
	{
		glBindTexture(GL_TEXTURE_2D, uiTextures[i]);

		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://在三線性過濾的模式下開啓各項異性過濾就會發現計算很遠距離的仍然能看到磚縫
			if (gltIsExtSupported("GL_EXT_texture_filter_anisotropic"))
			{
				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;
		default:
			break;
		}
	}

	glutPostRedisplay();

}


void SetupRC(void)
{
	shaderManager.InitializeStockShaders();

	glGenTextures(TEXTURE_COUNT, uiTextures);

	GLbyte *pBits;
	int nWidth, nHeight, nComponents;
	GLenum eFormat;
	
	for (size_t i = 0; i < TEXTURE_COUNT; ++i)
	{
		glBindTexture(GL_TEXTURE_2D, uiTextures[i]);
		// Read the texture bits
		pBits = gltReadTGABits(uiTextureName[i], &nWidth, &nHeight, &nComponents, &eFormat);
		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, nComponents, nWidth, nHeight, 0, eFormat, GL_UNSIGNED_BYTE, pBits);
		glGenerateMipmap(GL_TEXTURE_2D);
		free(pBits);
	}

	glClearColor(0.0f,0.0f,0.0f,1.0f);

	GLfloat z;
	floorBatch.Begin(GL_TRIANGLE_STRIP, 28,1);
	for (z = 60.f; z >= 0.0f; z -= 10.0f)
	{
		floorBatch.Normal3f(0.0f, 1.0f, 0.0f);
		floorBatch.MultiTexCoord2f(0, 0.0f, 0.0f);
		floorBatch.Vertex3f(-10.0f, -10.0f, z);

		floorBatch.Normal3f(0.0f, 1.0f, 0.0f);
		floorBatch.MultiTexCoord2f(0, 1.0f, 0.0f);
		floorBatch.Vertex3f(10.0f, -10.0f, z);

		floorBatch.Normal3f(0.0f, 1.0f, 0.0f);
		floorBatch.MultiTexCoord2f(0, 0.0f, 1.0f);
		floorBatch.Vertex3f(-10.0f, -10.0f, z - 10.0f);

		floorBatch.Normal3f(0.0f, 1.0f, 0.0f);
		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);// 哪裏來，哪裏回；根據法線來確認逆時針方向。strip的畫法要熟悉，從其實的兩個頂點開始已折線的形式前進
	for (z = 60.f; z >= 0.0f; z -= 10.0f)
	{
		ceilingBatch.Normal3f(0.0f, -1.0f, 0.0f);
		ceilingBatch.MultiTexCoord2f(0, 0.0f, 0.0f);
		ceilingBatch.Vertex3f(10.0f, 10.0f, z);

		ceilingBatch.Normal3f(0.0f, -1.0f, 0.0f);
		ceilingBatch.MultiTexCoord2f(0, 1.0f, 0.0f);
		ceilingBatch.Vertex3f(-10.0f, 10.0f, z);

		ceilingBatch.Normal3f(0.0f, -1.0f, 0.0f);
		ceilingBatch.MultiTexCoord2f(0, 1.0f, 1.0f);
		ceilingBatch.Vertex3f(10.0f, 10.0f, z - 10.0f);

		ceilingBatch.Normal3f(0.0f, -1.0f, 0.0f);
		ceilingBatch.MultiTexCoord2f(0, 0.0f, 1.0f);
		ceilingBatch.Vertex3f(-10.0f, 10.0f, z - 10.0f);
	}
	ceilingBatch.End();


	leftWallBatch.Begin(GL_TRIANGLE_STRIP, 28, 1);
	for (z = 60.f; z >= 0.0f; z -= 10.0f)
	{
		leftWallBatch.Normal3f(1.0f, 0.0f, 0.0f);
		leftWallBatch.MultiTexCoord2f(0, 0.0f, 1.0f);
		leftWallBatch.Vertex3f(-10.0f, 10.0f, z);

		leftWallBatch.Normal3f(1.0f, 0.0f, 0.0f);
		leftWallBatch.MultiTexCoord2f(0, 0.0f, 0.0f);
		leftWallBatch.Vertex3f(-10.0f, -10.0f, z);

		leftWallBatch.Normal3f(1.0f, 0.0f, 0.0f);
		leftWallBatch.MultiTexCoord2f(0, 1.0f, 1.0f);
		leftWallBatch.Vertex3f(-10.0f, 10.0f, z - 10.0f);

		leftWallBatch.Normal3f(1.0f, 0.0f, 0.0f);
		leftWallBatch.MultiTexCoord2f(0, 1.0f, 0.0f);
		leftWallBatch.Vertex3f(-10.0f, -10.0f, z - 10.0f);
	}
	leftWallBatch.End();


	rightWallBatch.Begin(GL_TRIANGLE_STRIP, 28, 1);
	for (z = 60.f; z >= 0.0f; z -= 10.0f)
	{
		rightWallBatch.Normal3f(-1.0f, 0.0f, 0.0f);
		rightWallBatch.MultiTexCoord2f(0, 1.0f, 0.0f);
		rightWallBatch.Vertex3f(10.0f, -10.0f, z);

		rightWallBatch.Normal3f(-1.0f, 0.0f, 0.0f);
		rightWallBatch.MultiTexCoord2f(0, 1.0f, 1.0f);
		rightWallBatch.Vertex3f(10.0f, 10.0f, z);

		rightWallBatch.Normal3f(-1.0f, 0.0f, 0.0f);
		rightWallBatch.MultiTexCoord2f(0, 0.0f, 0.0f);
		rightWallBatch.Vertex3f(10.0f, -10.0f, z - 10.0f);

		rightWallBatch.Normal3f(-1.0f, 1.0f, 1.0f);
		rightWallBatch.MultiTexCoord2f(0, 0.0f, 1.0f);
		rightWallBatch.Vertex3f(10.0f, 10.0f, z - 10.0f);
	}
	rightWallBatch.End();
}

void RenderScene(void)
{
	glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);


	modelViewMatrix.PushMatrix();
	{

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

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

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

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

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

	modelViewMatrix.PopMatrix();

	glutSwapBuffers();
}

void SpecialKeys(int key, int x, int y)
{
	if (key == GLUT_KEY_UP)
	{
		viewZ += 0.5f;
	}

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

	glutPostRedisplay();
}

void ShutdownRC(void)
{
	glDeleteTextures(3, uiTextures);
}

int main(int argc, char * argv[])
{
	gltSetWorkingDirectory(argv[0]);

	glutInit(&argc, argv);
	glutInitDisplayMode(GL_DOUBLE | GL_DEPTH | GL_STENCIL);
	glutInitWindowSize(1440, 900);
	glutCreateWindow("Tunnel @Jingz");

	glutReshapeFunc(ChangeSize);
	glutDisplayFunc(RenderScene);
	glutSpecialFunc(SpecialKeys);

	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 (err != GLEW_OK)
	{
		fprintf(stderr, "GLEW ERROR: %s\n", glewGetErrorString(err));
	}

	SetupRC();

	glutMainLoop();

	ShutdownRC();

	return 0;
}