From 943e0d8bb6f808966f9ec783a5826fe2840c6545 Mon Sep 17 00:00:00 2001
From: Peter Wu <lekensteyn@gmail.com>
Date: Thu, 14 Nov 2013 21:12:08 +0100
Subject: Improved exercise 1.1 (axis)

Documented steps better, reduce code duplication.
---
 src/RobotRace.java | 77 ++++++++++++++++++++++++++++++++++++------------------
 1 file changed, 52 insertions(+), 25 deletions(-)

diff --git a/src/RobotRace.java b/src/RobotRace.java
index 28d4ca5..f9c1a0b 100644
--- a/src/RobotRace.java
+++ b/src/RobotRace.java
@@ -205,37 +205,64 @@ public class RobotRace extends Base {
         gl.glScalef(1f, 1f, 2f);
 
         // Translated, rotated, scaled box.
-        glut.glutWireCube(1f);                 
+        glut.glutWireCube(1f);
     }
-    
-    
+
+    /**
+     * Draw a colored arrow from left to right.
+     *
+     * @param r Red color scale (0 to 1).
+     * @param g Green color scale (0 to 1).
+     * @param b Blue color scale (0 to 1).
+     */
+    private void drawColoredArrow(float r, float g, float b) {
+        gl.glPushMatrix();
+
+        // change color
+        gl.glColor3f(r, g, b);
+
+        // draw a thin line from the origin to the right.
+        gl.glTranslatef(0.5f, 0, 0);
+        gl.glScalef(1f, 0.01f, 0.01f);
+        glut.glutSolidCube(1f);
+        // restore scale for clarity.
+        gl.glScalef(1f, 1/0.01f, 1/0.01f);
+
+        // draw a cone on the end of the line that has a head that has a radius
+        // which is three times larger than the line segment.
+        gl.glTranslatef(0.5f, 0, 0);
+        // turn head to the right (rotate 90 degree from the Y-axis)
+        gl.glRotatef(90, 0, 1, 0);
+        glut.glutSolidCone(.03f, .1f, 10, 10);
+
+        // restore previous matrix
+        gl.glPopMatrix();
+    }
+
     /**
      * Draws the x-axis (red), y-axis (green), z-axis (blue),
      * and origin (yellow).
      */
     public void drawAxisFrame() {
-        gl.glPushMatrix();
-        gl.glPushMatrix();
-        gl.glPushMatrix();
-        
-        gl.glColor3f(0f, 0f, 1f);
-        gl.glScalef(0.5f, 0.5f, 4f);
-        glut.glutSolidCube(0.5f);
-        
-        gl.glPopMatrix();
-        
-        gl.glColor3f(0f, 1f, 0f);
-        gl.glScalef(0.5f, 4f, 0.5f);
-        glut.glutSolidCube(0.5f);
-        
-        gl.glPopMatrix();
-        
-        gl.glColor3f(1f, 0f, 0f);
-        gl.glScalef(4f, 0.5f, 0.5f);
-        glut.glutSolidCube(0.5f);
-               
-        gl.glPopMatrix();
-        
+        // X-axis: normal orientation
+        drawColoredArrow(1, 0, 0);
+
+        // Y-axis: rotate 90 degree clockwise in the Z-axis
+        gl.glRotatef(90, 0, 0, 1);
+        drawColoredArrow(0, 1, 0);
+        gl.glRotatef(-90, 0, 0, 1);
+
+        // Z-axis: rotate 90 degree in the XY ais
+        gl.glRotatef(-90, 0, 1, 0);
+        drawColoredArrow(0, 0, 1);
+        gl.glRotatef(90, 0, 1, 0);
+
+        // yellow sphere of 0.03m (with ten divisions)
+        gl.glColor3f(1, 1, 0);
+        glut.glutSolidSphere(0.05f, 10, 10);
+
+        // reset color
+        gl.glColor3f(0, 0, 0);
     }
     
     /**
-- 
cgit v1.2.1