c++ - 移动时使正方形变大

Question

#include <stdio.h> // this library is for standard input and output
#include "glut.h" // this library is for glut the OpenGL Utility Toolkit
#include <math.h>

float squareX = 0.0f;
float squareY = 200.0f;

static int flag = 1;

void drawShape(void) {
    float width = 58.0f;
    float height = 40.0f;
    glTranslatef(squareX, squareY, 0);
    // test
    // glScalef(0.0, 0.0, 0.0);
    glBegin(GL_POLYGON);
    glColor3f(1.0, 0.0, 0.0);
    glVertex2f(0, 0);
    glVertex2f(width, 0);
    glVertex2f(width, height);
    glVertex2f(0, height);
    glVertex2f(0, 0);
    glEnd();
}

void initRendering() {
    glEnable(GL_DEPTH_TEST);
}

// called when the window is resized
void handleResize(int w, int h) {
    glViewport(0, 0, w, h);
    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();
    glOrtho(0.0f, (float)w, 0.0f, (float)h, -1.0f, 1.0f);
}

int state = 1;

void update(int value) {
    if (state == 1) { // 1 : move right
        squareX += 1.0f;
        if (squareX > 400.0) {
            state = 0;
        }
    }
    glutPostRedisplay();
    glutTimerFunc(25, update, 0);
}

void display() {
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity();
    drawShape();
    glutSwapBuffers();
}

int main(int argc, char** argv) {
    glutInit(&argc, argv);
    glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGB | GLUT_DEPTH);
    glutInitWindowSize(400, 400);
    glutCreateWindow("Moving Square");
    initRendering();
    glutDisplayFunc(display);
    glutReshapeFunc(handleResize);
    glutTimerFunc(25, update, 0);
    glutMainLoop();
    return(0);
}

我想让正方形在向右移动时变大。请参阅下面的第二个 GIF。我知道我需要 glScalef 来使正方形变大，但我不知道如何在它移动时使其变大。

代码预览:

我需要它来做类似的事情(对质量感到抱歉，我自己创建了 GIF):

Answer 1

使用glScale根据 X 位置缩放矩形 (squareX):

float rectScale = 1.0f + (squareX / 400.0f);
glScalef(rectScale, rectScale, 1.0f);

注意 squareX 的范围是 [0.0, 400.0]，所以 1.0f + (squareX/400.0f) 的范围是 [1.0, 2.0]。

首先，缩放必须应用于矩形。这意味着它必须是在绘制矩形之前应用于模型 View 矩阵的最后一个操作。最终函数 drawShape 可能如下所示:

void drawShape(void) {
    float width = 58.0f;
    float height = 40.0f;
    glTranslatef(squareX, squareY, 0);

    float rectScale = 1.0f + (squareX / 400.0f);
    glScalef(rectScale, rectScale, 1.0f);

    glBegin(GL_POLYGON);
    glColor3f(1.0, 0.0, 0.0);
    glVertex2f(0, 0);
    glVertex2f(width, 0);
    glVertex2f(width, height);
    glVertex2f(0, height);
    glVertex2f(0, 0);
    glEnd();
}

预览: