在完成所有绘图代码后,是否需要重复glOrtho调用？

Question

我用OpenGL创建2D游戏.每次我移动我的对象时,我都要调用glLoadIdentity,因为否则所有对象都会移动,但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();
}

如何正确完成,显示,移动和旋转已glOrtho启用的对象？

Answer 1

但是glLoadIdentity也会重置glOrtho调用,所以基本上我以这样的结尾

glOrtho属于投影矩阵,而不属于modelview矩阵.你接受的答案在概念上并没有错,但确实错过了那一部分.代码的那部分应该是这样的

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();