在OpenGL中更改投影 [英] Changing projection in OpenGL

问题描述

我无法调整GLUT窗口的大小.我想打印一个矩形，但是当我使用调整大小功能时，我似乎无法在窗口中绘制形状.我有以下代码，当我调整窗口大小时，我想随正方形的宽度而改变，但是如果改变高度，我不希望它的高度改变.

I'm having trouble with resizing a GLUT window. I want to print a rectangle but when i use the resize function i cant seem to draw and shape in the window. I have the following code and i want to change with width of the square when i resize the window but if the height is resized i dont want the height of it to change.

#include <GLUT/glut.h>
#include <stdio.h>
#include <stdlib.h>
/* globals */
GLsizei wh = 500, ww = 500; 
/* initial window size */ 
GLfloat size = 3.0; 
/* half side length of square */

void myinit(void)
{
    glClearColor(0.0,0.0,1.0,1.0);
    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();
    glOrtho(0,1,0,1.0,-1.0,1.0);
    glViewport(0,0,ww,wh);
}

/* display callback -- required by GLUT 3.0 */
void renderScene(void)
{
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
    glColor3f(1.0,.5,.7);
    glBegin(GL_POLYGON);
        glVertex3f (0.25, 0.25, 0.0);
        glVertex3f (0.75, 0.25, 0.0);
        glVertex3f (0.75, 0.75, 0.0);
        glVertex3f (0.25, 0.75, 0.0);
    glEnd();

    glFlush();
}

void mouse(int button, int state, int x, int y) {
    if(button == GLUT_RIGHT_BUTTON && state == GLUT_DOWN) {
       glMatrixMode(GL_PROJECTION);
       glLoadIdentity();
       glOrtho(0.0,500,0.0,500,0.0,1.0);
   }
}
/*app quits if q is pressed*/
void keyboard(unsigned char key, int x, int y) {
     if(key == 'Q' | key == 'q')
        exit(0);
}

/* The main program -- note that there is no "flow of control" -- the program merely calls          functions to handle interactions */
int main(int argc, char** argv)
{
    glutInit(&argc, argv);
    glutInitWindowSize(ww,wh);
    glutInitWindowPosition(100,100);
    glutCreateWindow("Square");

    myinit();

    glutMouseFunc(mouse);
    glutKeyboardFunc(keyboard);
    glutDisplayFunc(renderScene);
    //glutReshapeFunc(changeSize);
    glutMainLoop();
    return 0;
}

我做了一个测试changeSize函数，当我使用它时，它将显示一个空的蓝色窗口，里面没有矩形

i made a test changeSize function and when i used that it would just show an empty blue window without the rectangle in there

推荐答案

您的问题在于对正交矩阵使用固定值:

Your problem lies in the use of a fixed value for the orthographic matrix:

glOrtho(0.0,500,0.0,500,0.0,1.0);

这表示，无论我的窗口有多大，将0的顶点位置映射到窗口底部，而将500的顶点位置映射到窗口顶部.

What this says is, however big my window is, make vertex position of 0 map to the bottom of the window, and 500 map to the top of the window.

因此，如果您有一个500像素高的窗口，并绘制一个覆盖100个单位的正方形，它将映射到该窗口中的100像素.

So if you have a 500 pixel high window, and you draw a square that covers 100 units, this will map to 100 pixels in the window.

但是，如果将窗口拉伸到1000像素高，现在将有一个从0到500的区域映射到一个高度为1000像素的窗口.因此，您以前可以覆盖100个像素的正方形现在覆盖了200个像素.

However if you stretch the window to be 1000 pixels high, now you have a region from 0 to 500 mapping to a window of height 1000 pixels. So your same square that used to cover 100 pixels in height now covers 200 pixels in height.

如果希望在调整大小时始终保持相同大小，则需要更新正交矩阵以将更大的区域映射到新的更大的窗口.因此，如果更改正交矩阵以将区域0 to windowHeight映射到窗口，则100个单位的正方形将始终填充完全相同的高度.

If you want it to always be the same size when you resize, you need to update the orthographic matrix to map a larger area to the new larger window. So if you change your orthographic matrix to map region 0 to windowHeight to the window, a 100 unit square will always fill the exact same amount of height.

glOrtho( 0.0, //left
         500, //right
         0.0, //bottom
         height_in_pixels, //top
         0.0,   //near 
         1.0);  //far

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