Question

我正在尝试创建一个400x300的屏幕，其中一条线从点（180,15）到点（10,145）。这是我的显示功能，我在其中创建了一行：

@Override
public void display(GLAutoDrawable drawable) {
  GL2 gl = drawable.getGL().getGL2();  // get the OpenGL 2 graphics context
  gl.glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT); // clear color and depth buffers
  gl.glLoadIdentity();  // reset the model-view matrix


  gl.glColor3f(1.0f, 0.0f, 0.0f);  //set color of line
  gl.glTranslatef(0.0f, 0.0f, -6.0f); // translate into the screen
  gl.glBegin(GL_LINES); 
    gl.glVertex2f(180, 15); //specify line-segment geometry must use relative values
    gl.glVertex2f(10,145);
  gl.glEnd();

  gl.glFlush();
}

这是init函数，我首先定义屏幕的正交参数：

@Override
public void init(GLAutoDrawable drawable) {
    GL2 gl = (GL2) drawable.getGL();    // get the OpenGL graphics context
    drawable.setGL(new DebugGL2(gl));   //set debugger. This will come in handy.
    glu = new GLU();                         // get GL Utilities
    gl.glClearDepth(1.0f);      // set clear depth value to farthest
    gl.glEnable(GL_DEPTH_TEST); // enables depth testing
    gl.glClearColor(1.0f, 1.0f, 1.0f, 0.0f); // sets base color for glClear()
    gl.glDepthFunc(GL_LEQUAL);  // the type of depth test to do
    gl.glHint(GL_PERSPECTIVE_CORRECTION_HINT, GL_NICEST); // best perspective correction
    gl.glShadeModel(GL_SMOOTH); // blends colors nicely, and smoothes out lighting

    //orthographic parameters set here
    glu.gluOrtho2D(0, 200, 0, 150);

}

这是调整查看屏幕大小时调用的重塑函数（根据我的理解）。

@Override
public void reshape(GLAutoDrawable drawable, int x, int y, int width, int height) {
    GL2 gl = drawable.getGL().getGL2();  // get the OpenGL 2 graphics context

    if (height == 0) height = 1;   // prevent divide by zero
    float aspect = (float)width / height;
    glu = new GLU();

    // Set the view port (display area) to cover the entire window
    gl.glViewport(0, 0, width, height);

    // Setup perspective projection, with aspect ratio matches viewport
    glu.gluOrtho2D(0, 200, 0, 150); //set 2-D orthographic context

    glu.gluPerspective(45.0, aspect, 0.1, 100.0); // fovy, aspect, zNear, zFar


    // Enable the model-view transform
    gl.glMatrixMode(GL_MODELVIEW);
    gl.glLoadIdentity(); // reset

}

我也尝试过使用：

gl.glMatrixMode(GL_PROJECTION);
gl.glOrtho(0,200,150,0,-1,1);

和

gl.glMatrixMode(GL_PROJECTION);
gl.glOrtho(-1,1,-1,1,-1,1);

即使用相对比例。但是，我所做的一切似乎都无法发挥作用。

Answer 1

在要绘制的窗口中设置区域或视口

gl.glViewport(0, 0, width, height); //in pixels

设置投影，使OpenGL坐标以像素为单位（与视口的宽度/高度相匹配）

//we want to modify the projection matrix (without this, mesh normals will break)
gl.glMatrixMode(GL_PROJECTION);

//clear any previous transforms the projection matrix may contain (otherwise it would be combined with the following glOrtho matrix)
gl.glLoadIdentity();

//set the projection (could use glTranslate/glScale but this utility function is simpler)
gl.glOrtho(0, width, 0, height, -1, 1); //left,right,bottom,top,front,back

//common practice to leave modelview as the current matrix for editing
gl.glMatrixMode(GL_MODELVIEW);

现在观看量是由glOrtho定义的框。

请注意，(0, 0)目前位于左下方。如果你正在做任何GUI的东西，那么当我们从左到右阅读时，翻转它并使原点左上方是非常有用的。没有什么可以阻止你改变绘图的一半 - 用一些任意坐标系统做一些3D东西，然后画一个HUD并设置投影以匹配像素。

在你的显示功能中绘制你的线......

gl.glBegin(GL_LINES); 
gl.glVertex2f(180, 15);
gl.glVertex2f(10,145);
gl.glEnd();

或，以演示使用翻译

gl.glLoadIdentity(); //remove the following translate that's still in the modelview matrix from the previous display() call
gl.glTranslatef(180, 15); //modifies the modelview matrix
gl.glBegin(GL_LINES); 
gl.glVertex2f(0, 0);
gl.glVertex2f(-170, 130);
gl.glEnd();

您可以考虑将视图向下移动到左侧，或者将模型（线）向上移动到右侧

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在OpenGL中绘制一条以像素为单位的坐标线

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