的Box2D/OpenGL的：一個紋理貼圖許多頂點

Question

我試圖做這樣的對象與Box2D的：Wobbly Picture using Box2D

建設有身體和關節電網是沒有問題的，但我想用這矩陣的點扭曲我的形象。問題是我不知道如何「剪切」我的紋理並將其映射到OpenGL頂點數組上。我聽說過u和v座標，但紋理裁剪呢？

Answer 1

既然你是問如何連接的紋理，來看看這個修改的this hane lesson：

// 
// This code was created by Jeff Molofee '99 (ported to Linux/GLUT by Richard Campbell '99) 
// 
// If you've found this code useful, please let me know. 
// 
// Visit me at www.demonews.com/hosted/nehe 
// (email Richard Campbell at ulmont@bellsouth.net) 
// 
#include <GL/glut.h> // Header File For The GLUT Library 
#include <GL/gl.h> // Header File For The OpenGL32 Library 
#include <GL/glu.h> // Header File For The GLu32 Library 
#include <stdio.h>  // Header file for standard file i/o. 
#include <stdlib.h>  // Header file for malloc/free. 
#include <unistd.h>  // needed to sleep. 

/* ascii code for the escape key */ 
#define ESCAPE 27 

/* The number of our GLUT window */ 
int window; 

/* floats for x rotation, y rotation, z rotation */ 
float xrot, yrot, zrot; 

/* storage for one texture */ 
int texture[1]; 

/* Image type - contains height, width, and data */ 
struct Image { 
    unsigned long sizeX; 
    unsigned long sizeY; 
    char *data; 
}; 
typedef struct Image Image; 

// quick and dirty bitmap loader...for 24 bit bitmaps with 1 plane only. 
// See http://www.dcs.ed.ac.uk/~mxr/gfx/2d/BMP.txt for more info. 
int ImageLoad(char *filename, Image *image) { 
    FILE *file; 
    unsigned long size;     // size of the image in bytes. 
    unsigned long i;     // standard counter. 
    unsigned short int planes;   // number of planes in image (must be 1) 
    unsigned short int bpp;    // number of bits per pixel (must be 24) 
    char temp;       // temporary color storage for bgr-rgb conversion. 

    // make sure the file is there. 
    if ((file = fopen(filename, "rb"))==NULL) 
    { 
    printf("File Not Found : %s\n",filename); 
    return 0; 
    } 

    // seek through the bmp header, up to the width/height: 
    fseek(file, 18, SEEK_CUR); 

    // read the width 
    if ((i = fread(&image->sizeX, 4, 1, file)) != 1) { 
    printf("Error reading width from %s.\n", filename); 
    return 0; 
    } 
    printf("Width of %s: %lu\n", filename, image->sizeX); 

    // read the height 
    if ((i = fread(&image->sizeY, 4, 1, file)) != 1) { 
    printf("Error reading height from %s.\n", filename); 
    return 0; 
    } 
    printf("Height of %s: %lu\n", filename, image->sizeY); 

    // calculate the size (assuming 24 bits or 3 bytes per pixel). 
    size = image->sizeX * image->sizeY * 3; 

    // read the planes 
    if ((fread(&planes, 2, 1, file)) != 1) { 
    printf("Error reading planes from %s.\n", filename); 
    return 0; 
    } 
    if (planes != 1) { 
    printf("Planes from %s is not 1: %u\n", filename, planes); 
    return 0; 
    } 

    // read the bpp 
    if ((i = fread(&bpp, 2, 1, file)) != 1) { 
    printf("Error reading bpp from %s.\n", filename); 
    return 0; 
    } 
    if (bpp != 24) { 
    printf("Bpp from %s is not 24: %u\n", filename, bpp); 
    return 0; 
    } 

    // seek past the rest of the bitmap header. 
    fseek(file, 24, SEEK_CUR); 

    // read the data. 
    image->data = (char *) malloc(size); 
    if (image->data == NULL) { 
    printf("Error allocating memory for color-corrected image data"); 
    return 0; 
    } 

    if ((i = fread(image->data, size, 1, file)) != 1) { 
    printf("Error reading image data from %s.\n", filename); 
    return 0; 
    } 

    for (i=0;i<size;i+=3) { // reverse all of the colors. (bgr -> rgb) 
    temp = image->data[i]; 
    image->data[i] = image->data[i+2]; 
    image->data[i+2] = temp; 
    } 

    // we're done. 
    return 1; 
} 

// Load Bitmaps And Convert To Textures 
void LoadGLTextures() { 
    // Load Texture 
    Image *image1; 

    // allocate space for texture 
    image1 = (Image *) malloc(sizeof(Image)); 
    if (image1 == NULL) { 
    printf("Error allocating space for image"); 
    exit(0); 
    } 

    if (!ImageLoad("Data/lesson6/NeHe.bmp", image1)) { 
    exit(1); 
    } 

    // Create Texture 
    glGenTextures(1, &texture[0]); 
    glBindTexture(GL_TEXTURE_2D, texture[0]); // 2d texture (x and y size) 

    glTexParameteri(GL_TEXTURE_2D,GL_TEXTURE_MAG_FILTER,GL_LINEAR); // scale linearly when image bigger than texture 
    glTexParameteri(GL_TEXTURE_2D,GL_TEXTURE_MIN_FILTER,GL_LINEAR); // scale linearly when image smalled than texture 

    // 2d texture, level of detail 0 (normal), 3 components (red, green, blue), x size from image, y size from image, 
    // border 0 (normal), rgb color data, unsigned byte data, and finally the data itself. 
    glTexImage2D(GL_TEXTURE_2D, 0, 3, image1->sizeX, image1->sizeY, 0, GL_RGB, GL_UNSIGNED_BYTE, image1->data); 
}; 

/* A general OpenGL initialization function. Sets all of the initial parameters. */ 
void InitGL(int Width, int Height)   // We call this right after our OpenGL window is created. 
{ 
    LoadGLTextures();    // Load The Texture(s) 
    glEnable(GL_TEXTURE_2D);   // Enable Texture Mapping 
    glClearColor(0.0f, 0.0f, 1.0f, 0.0f); // Clear The Background Color To Blue 
    glClearDepth(1.0);    // Enables Clearing Of The Depth Buffer 
    glDepthFunc(GL_LESS);   // The Type Of Depth Test To Do 
    glEnable(GL_DEPTH_TEST);   // Enables Depth Testing 
    glShadeModel(GL_SMOOTH);   // Enables Smooth Color Shading 

    glMatrixMode(GL_PROJECTION); 
    glLoadIdentity();    // Reset The Projection Matrix 

    gluPerspective(45.0f,(GLfloat)Width/(GLfloat)Height,0.1f,100.0f); // Calculate The Aspect Ratio Of The Window 

    glMatrixMode(GL_MODELVIEW); 
} 

/* The function called when our window is resized (which shouldn't happen, because we're fullscreen) */ 
void ReSizeGLScene(int Width, int Height) 
{ 
    if (Height==0)    // Prevent A Divide By Zero If The Window Is Too Small 
    Height=1; 

    glViewport(0, 0, Width, Height);  // Reset The Current Viewport And Perspective Transformation 

    glMatrixMode(GL_PROJECTION); 
    glLoadIdentity(); 

    gluPerspective(45.0f,(GLfloat)Width/(GLfloat)Height,0.1f,100.0f); 
    glMatrixMode(GL_MODELVIEW); 
} 

/* The main drawing function. */ 
void DrawGLScene() 
{ 
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);  // Clear The Screen And The Depth Buffer 
    glLoadIdentity();    // Reset The View 

    glTranslatef(0.0f,0.0f,-5.0f);    // move 5 units into the screen. 
    glRotatef(xrot,1.0f,0.0f,0.0f); 


    glBindTexture(GL_TEXTURE_2D, texture[0]); // choose the texture to use. 

    glBegin(GL_QUADS); 

    glTexCoord2f(0.0f, 0.0f); glVertex3f(-1.0f, -1.0f, 1.0f); 
    glTexCoord2f(0.5f, 0.0f); glVertex3f(0.0f, -1.0f, 1.0f); 
    glTexCoord2f(0.5f, 1.0f); glVertex3f(0.0f, 1.0f, 1.0f); 
    glTexCoord2f(0.0f, 1.0f); glVertex3f(-1.0f, 1.0f, 1.0f); 

    glTexCoord2f(0.5f, 0.0f); glVertex3f(0.0f, -1.0f, 1.0f); 
    glTexCoord2f(1.0f, 0.0f); glVertex3f(1.0f, -1.0f, 1.0f); 
    glTexCoord2f(1.0f, 1.0f); glVertex3f(1.0f, 1.0f, 1.0f); 
    glTexCoord2f(0.5f, 1.0f); glVertex3f(0.0f, 1.0f, 1.0f); 

    glEnd();         // done with the polygon. 

    xrot += 0.004; 

    // since this is double buffered, swap the buffers to display what just got drawn. 
    glutSwapBuffers(); 
} 

int main(int argc, char **argv) 
{ 
    /* Initialize GLUT state - glut will take any command line arguments that pertain to it or 
     X Windows - look at its documentation at http://reality.sgi.com/mjk/spec3/spec3.html */ 
    glutInit(&argc, argv); 

    /* Select type of Display mode: 
    Double buffer 
    RGBA color 
    Alpha components supported 
    Depth buffer */ 
    glutInitDisplayMode(GLUT_RGBA | GLUT_DOUBLE | GLUT_ALPHA | GLUT_DEPTH); 

    /* get a 640 x 480 window */ 
    glutInitWindowSize(640, 480); 

    /* the window starts at the upper left corner of the screen */ 
    glutInitWindowPosition(0, 0); 

    /* Open a window */ 
    window = glutCreateWindow("Jeff Molofee's GL Code Tutorial ... NeHe '99"); 

    /* Register the function to do all our OpenGL drawing. */ 
    glutDisplayFunc(&DrawGLScene); 

    /* Even if there are no events, redraw our gl scene. */ 
    glutIdleFunc(&DrawGLScene); 

    /* Register the function called when our window is resized. */ 
    glutReshapeFunc(&ReSizeGLScene); 

    /* Initialize our window. */ 
    InitGL(640, 480); 

    /* Start Event Processing Engine */ 
    glutMainLoop(); 
} 

具體來說，到DrawGLScene()功能，在那裏我四分裂成2個，並記錄有關紋理座標。