c++ - 我是否需要在所有绘图代码之后重复 glOrtho 调用？

Question

我正在使用 OpenGL 创建 2D 游戏。每次我移动对象时，我都必须调用 glLoadIdentity，否则所有对象都会被移动，但是 glLoadIdentity 也会重置 glOrtho 调用，所以基本上我以这样的结尾:

#include <GL/glfw.h>

int main()
{
glfwInit();

glfwOpenWindowHint( GLFW_WINDOW_NO_RESIZE, GL_TRUE );
glfwOpenWindowHint( GLFW_FSAA_SAMPLES, 8 );
glfwOpenWindow( 800, 600, 0, 0, 255, 0, 32, 0, GLFW_WINDOW );

glfwSetWindowTitle( "title" );

glfwSwapInterval( 1 ); // also known as 'vsync'

glfwEnable( GLFW_KEY_REPEAT );
//glfwDisable( GLFW_MOUSE_CURSOR );

glOrtho(0.0, 1024, 768, 0, -1.0, 1.0); 
glMatrixMode( GL_MODELVIEW );

while( !glfwGetKey( GLFW_KEY_ESC ) )
{
    glClearColor(0.0, 0.0, 0.0, 0.0);
    glClear(GL_COLOR_BUFFER_BIT);

    glLoadIdentity();
    glOrtho(0.0, 1024, 768, 0, -1.0, 1.0); 

    glTranslatef( 100, 0, 0 );

    glColor3f(0.5f,0.5f,1.0f);
    glBegin(GL_POLYGON);
      glVertex2f(100, 100);
      glVertex2f(100, 250);
      glVertex2f(250, 250);
      glVertex2f(250, 100);
    glEnd();

    glLoadIdentity();
    glOrtho(0.0, 1024, 768, 0, -1.0, 1.0); 

    glRotatef( 25,0,0,1);

    glBegin(GL_POLYGON);
      glVertex2f(300, 300);
      glVertex2f(300, 450);
      glVertex2f(450, 450);
      glVertex2f(450, 300);
    glEnd();

    glFlush();

    glfwSwapBuffers();
}

glfwTerminate();
}

如何正确地显示、移动和旋转启用 glOrtho 的对象？

Answer 1

but glLoadIdentity also resets glOrtho call, so basically I ending with something like this

glOrtho 属于投影矩阵，不属于模型 View 矩阵。您接受的答案在概念上并没有错，但确实遗漏了那部分。你的那部分代码应该看起来像

glMatrixMode(GL_PROJECTION);
glLoadIdentity();
glOrtho(0.0, 1024, 768, 0, -1.0, 1.0); 

glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
glTranslatef( 100, 0, 0 );

glColor3f(0.5f,0.5f,1.0f);
glBegin(GL_POLYGON);
  glVertex2f(100, 100);
  glVertex2f(100, 250);
  glVertex2f(250, 250);
  glVertex2f(250, 100);
glEnd();

glLoadIdentity();

glRotatef( 25,0,0,1);

glBegin(GL_POLYGON);
  glVertex2f(300, 300);
  glVertex2f(300, 450);
  glVertex2f(450, 450);
  glVertex2f(450, 300);
glEnd();

glFlush();

glfwSwapBuffers();