主要处理了纹理贴图和顶点映射的关系。根据法线先确认环绕方向。然后根据绘制的primitive_type完成纹理顶点直接的映射。
哪里来，哪里回；根据法线来确认逆时针方向。strip的画法要熟悉，从其实的两个顶点开始已折线的形式前进
GL_TRIANGLES_STRIP是常用的绘制方式，在循环代码中使用四个顶点+循环控制量能完成大量的几何图形绘制。这里我犯了个错误，没意识到折线的的前进方向问题，导致纹理映射出现了偏差，一度去怀疑modelViewMatrix的配置是否正确。但是我发现原书中的代码没有使用法线去控制贴图顶点之前的关系，而是使用了相反的方向和对应的坐标，我是看不懂了，还是踏实得配置法线接着再执行的映射。
//在三线性过滤的模式下开启各项异性过滤就会发现计算很远距离的仍然能看到砖缝
这个就是各项异性的优势，但是使用普通的GL_LINEAR过滤就能有一个较好的视觉效果，虽然逼真度不是很高。
#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://在三线性过滤的模式下开启各项异性过滤就会发现计算很远距离的仍然能看到砖缝
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);// 哪里来，哪里回；根据法线来确认逆时针方向。strip的画法要熟悉，从其实的两个顶点开始已折线的形式前进
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;
}版权声明：本文为博主原创文章，未经博主允许不得转载。
OpenGL蓝宝书第五章5.4Tunnuel 纹理映射和过滤：较好的可读性代码
原文地址：http://blog.csdn.net/jingzhewangzi/article/details/46851069
