opengl 开发笔记-绘制纹理

• 数据定义

  static Color4F white_color = {1.0f,1.0f,1.0f,1.0f};
  
  static Vertex2F rect_vertexes [4] =
  {
      {100,50},{400,50},
      {100,280},{400,280}
  };
  
  static Vertex2F texture_coords [4] =
  {
      {0,1},{1,1},
      {0,0},{1,0},
  };
  
  static GLuint texture_id = 0 ;
  

  
  
• 加载png文件（加载png图片文件到内存,当前默认认为图片是32位的色彩，长宽都是2的n次方）

   
  unsigned char* read_png(const char* path,int& width,int& height){
  
      FILE* file = fopen(path, "rb");
  
      if (!file){
          return NULL;
      }
  
      png_structp png_ptr = png_create_read_struct(PNG_LIBPNG_VER_STRING, 0, 0, 0);
      png_infop info_ptr = png_create_info_struct(png_ptr);
      setjmp(png_jmpbuf(png_ptr));
  
      png_init_io(png_ptr, file);
      png_read_png(png_ptr, info_ptr, PNG_TRANSFORM_EXPAND, 0);
  
      width = png_get_image_width(png_ptr,info_ptr);
      height = png_get_image_height(png_ptr,info_ptr);
      int color_type = png_get_color_type(png_ptr,info_ptr);
  
      int size = width * height * 4;
      unsigned char* data = new unsigned char[size];
      png_bytep* row_pointers = png_get_rows(png_ptr,info_ptr);
  
      int pos = 0;
      for(int i = 0; i < height; i++){
          for(int j = 0; j < (4 * width); j += 4){
              data[pos++] = row_pointers[i][j];   // red
              data[pos++] = row_pointers[i][j + 1]; // green
              data[pos++] = row_pointers[i][j + 2]; // blue
              data[pos++] = row_pointers[i][j + 3]; // alpha
              if(data[pos] !=0)
              printf("alpha=%d\n",data[pos]);
          }
      }
  
      png_destroy_read_struct(&png_ptr, &info_ptr, 0);
      fclose(file);
  
      return data;
  }
  

  
  
• 生成纹理

  GLuint init_texture(unsigned char* data,int width,int height){
      GLuint texName;
      glGenTextures(1, &texName);
  
      glBindTexture(GL_TEXTURE_2D, texName);
      glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
      glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
      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, GL_RGBA, width, height, 0, GL_RGBA, GL_UNSIGNED_BYTE, data);
  
      return texName;
  }
  

• 加载纹理

  GLuint load_texture(const char* path){
      GLuint tex_id = 0;
      int width,height;
      unsigned char* data = read_png(path,width,height);
  
      if(data != NULL){
          tex_id = init_texture(data,width,height);
          delete[] data;
          data = NULL;
      }
  
      return tex_id;
  }
  

• 显示纹理

  void draw_texture(){
      glEnableClientState(GL_VERTEX_ARRAY);
      glEnableClientState(GL_TEXTURE_COORD_ARRAY);
  
      glEnable(GL_TEXTURE_2D);
      glBindTexture(GL_TEXTURE_2D,texture_id);
      glTexCoordPointer(sizeof(Vertex2F)/sizeof(GLfloat),GL_FLOAT,0,texture_coords);
  
      glColor4f(white_color.r,white_color.g,white_color.b,white_color.a);
      glVertexPointer(sizeof(Vertex2F)/sizeof(GLfloat),GL_FLOAT,0,rect_vertexes);
  
      glDrawArrays(GL_TRIANGLE_STRIP,0,4);
  
      glDisable(GL_TEXTURE_2D);
      glDisableClientState(GL_TEXTURE_COORD_ARRAY);
      glDisableClientState(GL_VERTEX_ARRAY);
  }
  

• 编译程序

  g++ DrawTextures.cpp -lGLEW -lGL -lGLU -lglut -lpng -o DrawTextures

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