Why does my drawRect code always displays black

Question

This is my drawRect code:

    public static void drawRect(float X, float Y, float WIDTH, float HEIGHT, float RED, float GREEN, float BLUE)
    {
        // clear the screen and depth buffer
        GL11.glClear(GL11.GL_COLOR_BUFFER_BIT | GL11.GL_DEPTH_BUFFER_BIT); 
                 
        // set the color of the quad (R,G,B,A)
        GL11.glColor3f(RED, GREEN, BLUE);
             
        // draw quad
        GL11.glBegin(GL11.GL_QUADS);
        GL11.glVertex2f(X,Y);
        GL11.glVertex2f(X+WIDTH,Y);
        GL11.glVertex2f(X+WIDTH,Y+HEIGHT);
        GL11.glVertex2f(X,Y+HEIGHT);
        GL11.glEnd();
    }

This is what i'm doing

Renderer.drawRect(0, 0, Display.getWidth(), Display.getHeight(), 255, 255, 255);

It fills the entire screen (like it should) but the color is always black.

Does this answer your question? [LWJGL Tutorials](https://stackoverflow.com/questions/10126555/lwjgl-tutorials) — tevemadar, Jun 26 '20 at 19:42
Have you tried using color values between 0 and 1, instead of 0 to 255? They're floats after all — nylanderDev, Jun 26 '20 at 23:50
tevemadar, this does not answer my question but thank you for suggesting. — chai, Jun 27 '20 at 09:09
nylanderdev, yes. I tried setting all of the values to 1 but it's still black. — chai, Jun 27 '20 at 09:10

score 0 · Answer 1 · answered Jun 28 '20 at 11:13

I suggested reading tutorials because glColor3f() expects 3 floats in the 0...1 range for color components, just like most accelerated graphics API-s. And if this one slipped, there may be confusion about other details too. But nevertheless, 255 would be still clamped to 1, so the routine does not draw a black rectangle, something is missing before (in the setup) and/or after (like a call making the drawing actually appear on screen).

LWJGL wiki has a complete example code for exactly what you are trying to do, by the way: http://wiki.lwjgl.org/wiki/LWJGL_Basics_3_(The_Quad).html

import org.lwjgl.LWJGLException;
import org.lwjgl.opengl.Display;
import org.lwjgl.opengl.DisplayMode;
import org.lwjgl.opengl.GL11;
  
public class QuadExample {
  
    public void start() {
        try {
        Display.setDisplayMode(new DisplayMode(800,600));
        Display.create();
    } catch (LWJGLException e) {
        e.printStackTrace();
        System.exit(0);
    }
  
    // init OpenGL
    GL11.glMatrixMode(GL11.GL_PROJECTION);
    GL11.glLoadIdentity();
    GL11.glOrtho(0, 800, 0, 600, 1, -1);
    GL11.glMatrixMode(GL11.GL_MODELVIEW);
  
    while (!Display.isCloseRequested()) {
        // Clear the screen and depth buffer
        GL11.glClear(GL11.GL_COLOR_BUFFER_BIT | GL11.GL_DEPTH_BUFFER_BIT);  
         
        // set the color of the quad (R,G,B,A)
        GL11.glColor3f(0.5f,0.5f,1.0f);
             
        // draw quad
        GL11.glBegin(GL11.GL_QUADS);
            GL11.glVertex2f(100,100);
        GL11.glVertex2f(100+200,100);
        GL11.glVertex2f(100+200,100+200);
        GL11.glVertex2f(100,100+200);
        GL11.glEnd();
  
        Display.update();
    }
  
    Display.destroy();
    }
  
    public static void main(String[] argv) {
        QuadExample quadExample = new QuadExample();
        quadExample.start();
    }
}

Why does my drawRect code always displays black

1 Answers1