2

最近我一直在研究 OpenGL，如果我想对事物进行纹理处理，我已经上台了。我想我会从纹理一个简单的立方体开始。我目前有这段代码，并且完全理解它是如何工作的：

#include <glut.h>

#define WINDOW_WIDTH 400
#define WINDOW_HEIGHT 400


float angle = 30.0f;

void Draw() {

  glLoadIdentity(); //Reset the drawing perspective
  glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT); //Clears the buffers

  //Add positioned light
  GLfloat lightColor0[] = {0.5f, 0.5f, 0.5f, 1.0f}; //Color intensity
  GLfloat lightPos0[] = {0.0f, 0.0f, 0.0f, 1.0f}; //Positioned at..
  glLightfv(GL_LIGHT0, GL_DIFFUSE, lightColor0); //Set our light colour
  glLightfv(GL_LIGHT0, GL_POSITION, lightPos0); //Set our light position

  glMaterialf(GL_FRONT_AND_BACK, GL_SHININESS, 200);

  glRotatef(angle,1.0f,1.0f,1.0f); //Rotate around the origin
  glScalef(0.4f, 0.4f, 0.4f); //Scale the shape down
  glBegin(GL_QUADS); //Start drawing a Quad
  glColor3f(1.0f,0.0f,0.0f); //Set the colour to Red
  glVertex3f( 1.0f, 1.0f,-1.0f); //Top right of the quad (Top Face)
  glVertex3f(-1.0f, 1.0f,-1.0f); //Top left of the quad (Top Face)
  glVertex3f(-1.0f, 1.0f, 1.0f); //Bottom left of the quad (Top Face)
  glVertex3f( 1.0f, 1.0f, 1.0f); //Bottom right of the quad (Top Face)
  glVertex3f( 1.0f,-1.0f, 1.0f); //Top right of the quad (Bottom Face)
  glVertex3f(-1.0f,-1.0f, 1.0f); //Top left of the quad (Bottom Face)
  glVertex3f(-1.0f,-1.0f,-1.0f); //Bottom left of the quad (Bottom Face)
  glVertex3f( 1.0f,-1.0f,-1.0f); //Bottom right of the quad (Bottom Face)
  glVertex3f( 1.0f, 1.0f, 1.0f); //Top right of the quad (Front Face)
  glVertex3f(-1.0f, 1.0f, 1.0f); //Top left of the quad (Front Face)
  glVertex3f(-1.0f,-1.0f, 1.0f); //Bottom left of the quad (Front Face)
  glVertex3f( 1.0f,-1.0f, 1.0f); //Bottom right of the quad (Front Face)
  glVertex3f( 1.0f,-1.0f,-1.0f); //Top right of the quad (Back Face)
  glVertex3f(-1.0f,-1.0f,-1.0f); //Top left of the quad (Back Face)
  glVertex3f(-1.0f, 1.0f,-1.0f); //Bottom left of the quad (Back Face)
  glVertex3f( 1.0f, 1.0f,-1.0f); //Bottom right of the quad (Back Face)
  glVertex3f(-1.0f, 1.0f, 1.0f); //Top right of the quad (Left Face)
  glVertex3f(-1.0f, 1.0f,-1.0f); //Top left of the quad (Left Face)
  glVertex3f(-1.0f,-1.0f,-1.0f); //Bottom left of the quad (Left Face)
  glVertex3f(-1.0f,-1.0f, 1.0f); //Bottom right of the quad (Left Face)
  glVertex3f( 1.0f, 1.0f,-1.0f); //Top right of the quad (Right Face)
  glVertex3f( 1.0f, 1.0f, 1.0f); //Top left of the quad (Right Face)
  glVertex3f( 1.0f,-1.0f, 1.0f); //Bottom left of the quad (Right Face)
  glVertex3f( 1.0f,-1.0f,-1.0f); //Bottom right of the quad (Right Face)
  glEnd(); //Finished Drawing The Quad
  glutSwapBuffers(); //Send the 3D scene to the screen
}

void Update(int value){ //Our update function
  angle+=0.5f; //Increase the angle by 5

  if(angle>360){ //If the angle is greater than 360
    angle=0; //Set the angle to 0
  }

  glutPostRedisplay(); //Tell it that the scene has changed
  glutTimerFunc(25,Update,0); //Call "Update" again in another 25ms
}

void Initialize() {
  glEnable(GL_DEPTH_TEST);
  glEnable(GL_COLOR_MATERIAL);
  glEnable(GL_LIGHTING); //Enable lighting
  glEnable(GL_LIGHT0); //Enable light No. 0
  glEnable(GL_NORMALIZE); //Automatically "normalize" normals
  glShadeModel(GL_SMOOTH); //Enable smooth shading (nice effect)  

  glClearColor(0.0, 0.0, 0.0, 0.0); //Background RGBA
  glMatrixMode(GL_MODELVIEW); //MODELVIEW view
  glLoadIdentity(); //Start at origin
  glOrtho(0.0, 1.0, 0.0, 1.0, -1.0, 1.0); //Set the scale
  //X axis = 0 to 1. Y = 0 to 1. Z = -1 to 1.
}

int main() {
  glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGB | GLUT_DEPTH); //The display mode
  glutInitWindowSize(WINDOW_WIDTH, WINDOW_HEIGHT); //Window Size
  glutInitWindowPosition(200, 200); //Window Position
  glutCreateWindow("Lighting!"); //Creates a window with the name "Lighting!"
  Initialize(); //Call our initialize function.
  glutDisplayFunc(Draw); //"Draw" then refresh the window
  glutTimerFunc(25,Update,0); //Call "Update" 25ms after program starts
  glutMainLoop(); //Process events etc. Also keeps the window open.
  return 0; //End the program
}

然而，在阅读了许多纹理教程之后（我的意思是我可以在网上找到的所有教程）；我仍然对如何将其添加到该程序中感到困惑。我知道我必须（以某种方式）加载纹理，然后在绘制立方体之前使用 glBindTexture 函数绑定它，但我认为在这两者之间我还需要做一些其他事情（而且我不知道如何加载图像也正确）。

4

5 回答 5

3

要加载纹理文件（png、jpg...），请使用：（不要忘记安装 SDL 和 SDL_image 库）

#include <SDL/SDL.h>
#include <SDL/SDL_image.h>

GLuint texture_alloc(const char  *tex_name, int alpha)
{
    GLuint tex_num;

    SDL_Surface *tex_img;
    glGenTextures(1, &tex_num);

    if(tex_img = (SDL_Surface *) IMG_Load(tex_name)) {

        glBindTexture(GL_TEXTURE_2D, tex_num);
        glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
        glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR_MIPMAP_LINEAR);
        glTexParameteri(GL_TEXTURE_2D, GL_GENERATE_MIPMAP, GL_TRUE);

        if (alpha==1)
            glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, tex_img->w, tex_img->h, 0, GL_RGBA, GL_UNSIGNED_BYTE, tex_img->pixels);
        else
            glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, tex_img->w, tex_img->h, 0, GL_RGB, GL_UNSIGNED_BYTE, tex_img->pixels);
        SDL_FreeSurface (tex_img);
    }

    return tex_num;

}

要设置纹理坐标，请使用 glTexCoord 函数：

glTexCoord2f(0.0f, 0.0f);
glVertex3f( 1.0f, 1.0f,-1.0f); 
glTexCoord2f(1.0f, 0.0f);
glVertex3f(-1.0f, 1.0f,-1.0f);
.
.
.
于 2010-07-19T12:47:37.940 回答
2

我建议查看SOIL，一个 OpenGL 图像加载库 - 我使用它。

就获得纹理而言，它几乎是：

Unsigned int texture = SOIL_load_OGL_texture(imagePath.c_str(), SOIL_CREATE_NEW_ID, SOIL_LOAD_AUTO, SOIL_FLAG_MIPMAPS);

glBindTexture(texture);

但是，您必须使用纹理坐标，以便 opengl 知道如何包装您的纹理。下面是一些渲染多维数据集的示例调用。

    int size = 1;

    // Begin Rending
    glBegin(GL_QUADS);

    {
        // Face 1

        glNormal3f( 0.0f, 0.0f, 1.0f);  

        glTexCoord2f(0.0f, 0.0f);
        glVertex3f( m_size, m_size,-m_size);

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

        glTexCoord2f(1.0f, 1.0f);
        glVertex3f(-m_size, m_size, m_size);

        glTexCoord2f(0.0f, 1.0f);
        glVertex3f( m_size, m_size, m_size);    

        // Face 2

        glNormal3f( 0.0f, 0.0f,-1.0f);

        glTexCoord2f(0.0f, 0.0f);
        glVertex3f( m_size,-m_size, m_size);    

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

        glTexCoord2f(1.0f, 1.0f);
        glVertex3f(-m_size,-m_size,-m_size);

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

        // Face 3


        glTexCoord2f(0.0f, 0.0f);
        glVertex3f( m_size, m_size, m_size);    

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

        glTexCoord2f(1.0f, 1.0f);
        glVertex3f(-m_size,-m_size, m_size);    

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

        // Face 4

        glNormal3f( 0.0f,-1.0f, 0.0f);  

        glTexCoord2f(0.0f, 0.0f);
        glVertex3f( m_size,-m_size,-m_size);

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

        glTexCoord2f(1.0f, 1.0f);
        glVertex3f(-m_size, m_size,-m_size);

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

        // Face 5

        glNormal3f( 1.0f, 0.0f, 0.0f);

        glTexCoord2f(0.0f, 0.0f);
        glVertex3f(-m_size, m_size, m_size);    

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

        glTexCoord2f(1.0f, 1.0f);
        glVertex3f(-m_size,-m_size,-m_size);

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

        // Face 6

        glNormal3f( 1.0f, 0.0f, 0.0f);

        glTexCoord2f(0.0f, 0.0f);
        glVertex3f( m_size, m_size,-m_size);

        glTexCoord2f(1.0f, 0.0f);
        glVertex3f( m_size, m_size, m_size);

        glTexCoord2f(1.0f, 1.0f);
        glVertex3f( m_size,-m_size, m_size);

        glTexCoord2f(0.0f, 1.0f);
        glVertex3f( m_size,-m_size,-m_size);    
    }

    glEnd();
于 2010-07-17T11:54:40.300 回答
1

我认为您缺少的部分是纹理坐标的概念。

纹理是二维的吧？因此，当您将对象的 3d 点推送到图形卡时，如果您希望它具有纹理，您还需要将该 3d 点与纹理图像中的位置相关联，您可以使用一对纹理坐标（配对因为纹理是 2d)... 看看 glTexCoord2f()... 如果您在调用 glVertex3f() 之前调用它，您会将该 3d 点与图像中的一个点相关联... 如果您对构成原始opengl的所有点执行此操作，可以对中间的所有点进行插值...

于 2010-07-17T15:50:15.123 回答
0

对于图像加载，您还可以使用 SDL-image 库：

http://www.libsdl.org/projects/SDL_image/

它非常方便。

于 2010-07-17T12:37:41.053 回答
0

您可以使用来自http://nehe.gamedeve.net/的 glaux 代码，这也很简单。

AUX_RGBImageRec* LoadBMP(char* Filename)
{
    FILE *File = NULL;

    if ( !Filename )
        return NULL;

    File = fopen(Filename,"r");

    if ( !Filename )
        return NULL;

    fclose(File);
    return auxDIBImageLoad(Filename);
}

int LoadTextures()
{
    int Status = FALSE;
    AUX_RGBImageRec *TextureImage[1];
    memset(TextureImage,0,sizeof(void*)*1);

    if ( TextureImage[0] = LoadBMP("GoneFishing.bmp") )
    {
        Status = true;
        if(texture[0] == -1)
            glGenTextures(1,&texture[0]);
        glBindTexture(GL_TEXTURE_2D,texture[0]);
        // Generate The Texture
        glTexImage2D(GL_TEXTURE_2D, 0, 3, TextureImage[0]->sizeX, TextureImage[0]->sizeY, 0, GL_RGB, GL_UNSIGNED_BYTE, TextureImage[0]->data);
        glTexParameteri(GL_TEXTURE_2D,GL_TEXTURE_MIN_FILTER,GL_LINEAR); // Linear Filtering
        glTexParameteri(GL_TEXTURE_2D,GL_TEXTURE_MAG_FILTER,GL_LINEAR); // Linear Filtering
    }

    if (TextureImage[0])                            // If Texture Exists
    {
        if (TextureImage[0]->data)                  // If Texture Image Exists
        {
            free(TextureImage[0]->data);                // Free The Texture Image Memory
        }

        free(TextureImage[0]);                      // Free The Image Structure
    }

    return Status;
}
于 2010-07-20T06:58:40.597 回答