OpenGL多边形停留在左上角？

Question

我正在使用allegro库和OpenGL。我启用深度测试，然后在调整大小时执行以下操作：

    glEnable(GL_CULL_FACE);
    glCullFace(GL_BACK);
    glEnable(GL_DEPTH_TEST);
    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();
    glFrustum(0,event.display.width,event.display.height,0,1,300);

然后我的图像看起来像这样：

float BOX_SIZE = 200.0f;
        glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);


        glRotatef(0.5, 0, 0.0f, 1.0f);
        glBegin(GL_QUADS);

        //Top face
        glColor3f(1.0f, 1.0f, 0.0f);
        glNormal3f(0.0, 1.0f, 0.0f);
        glVertex3f(500 + -BOX_SIZE / 2, BOX_SIZE / 2, -BOX_SIZE / 2);
        glVertex3f(500 + -BOX_SIZE / 2, BOX_SIZE / 2, BOX_SIZE / 2);
        glVertex3f(500 + BOX_SIZE / 2, BOX_SIZE / 2, BOX_SIZE / 2);
        glVertex3f(500 + BOX_SIZE / 2, BOX_SIZE / 2, -BOX_SIZE / 2);

        //Bottom face
        glColor3f(1.0f, 0.0f, 1.0f);
        glNormal3f(0.0, -1.0f, 0.0f);
        glVertex3f(-BOX_SIZE / 2, -BOX_SIZE / 2, -BOX_SIZE / 2);
        glVertex3f(BOX_SIZE / 2, -BOX_SIZE / 2, -BOX_SIZE / 2);
        glVertex3f(BOX_SIZE / 2, -BOX_SIZE / 2, BOX_SIZE / 2);
        glVertex3f(-BOX_SIZE / 2, -BOX_SIZE / 2, BOX_SIZE / 2);

        //Left face
        glNormal3f(-1.0, 0.0f, 0.0f);
        glColor3f(0.0f, 1.0f, 1.0f);
        glVertex3f(-BOX_SIZE / 2, -BOX_SIZE / 2, -BOX_SIZE / 2);
        glVertex3f(-BOX_SIZE / 2, -BOX_SIZE / 2, BOX_SIZE / 2);
        glColor3f(0.0f, 0.0f, 1.0f);
        glVertex3f(-BOX_SIZE / 2, BOX_SIZE / 2, BOX_SIZE / 2);
        glVertex3f(-BOX_SIZE / 2, BOX_SIZE / 2, -BOX_SIZE / 2);

        //Right face
        glNormal3f(1.0, 0.0f, 0.0f);
        glColor3f(1.0f, 0.0f, 0.0f);
        glVertex3f(BOX_SIZE / 2, -BOX_SIZE / 2, -BOX_SIZE / 2);
        glVertex3f(BOX_SIZE / 2, BOX_SIZE / 2, -BOX_SIZE / 2);
        glColor3f(0.0f, 1.0f, 0.0f);
        glVertex3f(BOX_SIZE / 2, BOX_SIZE / 2, BOX_SIZE / 2);
        glVertex3f(BOX_SIZE / 2, -BOX_SIZE / 2, BOX_SIZE / 2);

        glEnd();

        glEnable(GL_TEXTURE_2D);

        glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
        glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
        glColor3f(1.0f, 1.0f, 1.0f);
        glBegin(GL_QUADS);

        //Front face
        glNormal3f(0.0, 0.0f, 1.0f);
        glTexCoord2f(0.0f, 0.0f);
        glVertex3f(-BOX_SIZE / 2, -BOX_SIZE / 2, BOX_SIZE / 2);
        glTexCoord2f(1.0f, 0.0f);
        glVertex3f(BOX_SIZE / 2, -BOX_SIZE / 2, BOX_SIZE / 2);
        glTexCoord2f(1.0f, 1.0f);
        glVertex3f(BOX_SIZE / 2, BOX_SIZE / 2, BOX_SIZE / 2);
        glTexCoord2f(0.0f, 1.0f);
        glVertex3f(-BOX_SIZE / 2, BOX_SIZE / 2, BOX_SIZE / 2);

        //Back face
        glNormal3f(0.0, 0.0f, -1.0f);
        glTexCoord2f(0.0f, 0.0f);
        glVertex3f(-BOX_SIZE / 2, -BOX_SIZE / 2, -BOX_SIZE / 2);
        glTexCoord2f(1.0f, 0.0f);
        glVertex3f(-BOX_SIZE / 2, BOX_SIZE / 2, -BOX_SIZE / 2);
        glTexCoord2f(1.0f, 1.0f);
        glVertex3f(BOX_SIZE / 2, BOX_SIZE / 2, -BOX_SIZE / 2);
        glTexCoord2f(0.0f, 1.0f);
        glVertex3f(BOX_SIZE / 2, -BOX_SIZE / 2, -BOX_SIZE / 2);

        glEnd();
        glDisable(GL_TEXTURE_2D);
 //code goes here
 al_flip_display();

由于某种原因，无论我如何翻译，立方体似乎总是从0,0延伸，并且始终存在一个顶点在0,0处。我做错了什么？谢谢。

- jmasterx

Answer 1

在阅读你的代码片段时，我不知道 Allegro 库的具体情况，但有两件事情需要注意。

1. 为什么你没有在调整大小时调用 glViewport(event.display.width,event.display.height)？通常，glFrustum 调用不应该依赖于显示器的大小。

2. 你是否曾经调用过 glMatrixMode(GL_MODELVIEW)？否则，所有矩阵操作都将应用于投影矩阵。

希望这可以帮到你。

- Greg S