Add the picking feature.

We can now select a LED on the screen and get the index of the LED.
To get the right index, we use the color picking technique mentioned
in the OpenGL RedBook. This works suprisingly pretty well (and fast!).

editor/src/config.h

@@ -10,8 +10,12 @@
 
 #define PI            3.1415926535897932
 
-#define TOP_ORIENTATION  1
-#define SIDE_ORIENTATION 2
+// Poor Man's enums
+#define TOP_ORIENTATION   0x01
+#define SIDE_ORIENTATION  0x02
+
+#define RENDER_MODE       0x01
+#define PICKING_MODE      0x02
 
 // Materials
 extern float ledOnMaterial[];

editor/src/display.c

@@ -5,21 +5,23 @@
 #include "display.h"
 
 
-void drawLEDCube(orientation) {
+void drawLEDs(int orientation, int mode) {
   int x, y, z;
+  int colorIndex = 0;
 
   if (orientation == TOP_ORIENTATION) {
     glRotatef(90, 2, 0, 0);
   }
 
-  // LEDs
-  glMaterialfv(GL_FRONT, GL_AMBIENT, ledOnMaterial);
   for (z=-10; z<=10; z+=10) // Ebene
     for (y=-10; y<=10; y+=10) // Zeile
       for (x=-10; x<=10; x+=10) { // Spalte
-
-        // TODO: Test different colors
+        if (mode == PICKING_MODE) {
+          glColor3ub(0, 0, colorIndex*8);
+          colorIndex++;
+        } else {
           glMaterialfv(GL_FRONT, GL_AMBIENT, (z == 0 ? ledOnMaterial : ledOffMaterial));
+        }
 
         glPushMatrix();
         glTranslatef(x, y, z-0.8);
@@ -35,8 +37,10 @@ void drawLEDCube(orientation) {
 
         glPopMatrix();
       }
+}
 
-  // Wires
+void drawWires() {
+  int x, y;
   for (y=-10; y<=10; y+=10)
     for (x=-10; x<=10; x+=10) {
       glMaterialfv(GL_FRONT, GL_AMBIENT, ((x == 0 || y == 0) ? innerWireMaterial : wireMaterial));
@@ -61,9 +65,8 @@ void drawLEDCube(orientation) {
     }
 }
 
-void display() {
+void setScene() {
   glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
-
   glMatrixMode(GL_PROJECTION);
   glLoadIdentity();
   gluPerspective(ZOOM_LEVEL, WINDOW_WIDTH/WINDOW_HEIGHT, 1.0, 350.0);
@@ -71,8 +74,25 @@ void display() {
   glMatrixMode(GL_MODELVIEW);
   glLoadIdentity();
   gluLookAt(lookX, eyeAngle, lookZ, 0, 0, 0, 0, 1, 0);
+}
 
-  drawLEDCube(TOP_ORIENTATION);
+// OpenGL Display function
+void display() {
+  setScene();
+  drawLEDs(TOP_ORIENTATION, RENDER_MODE);
+  drawWires();
   glutSwapBuffers();
 }
 
+// Picking function
+void displayPickingObjects() {
+  setScene();
+  glDisable(GL_DITHER);
+  glDisable(GL_LIGHTING);
+
+  drawLEDs(TOP_ORIENTATION, PICKING_MODE);
+
+  glEnable(GL_LIGHTING);
+  glEnable(GL_DITHER);
+}
+

editor/src/display.h

@@ -2,8 +2,13 @@
 #define _DISPLAY_H
 
 
-void drawLEDCube();
+void drawLEDs(int orientation, int mode);
+void drawWires();
+
 void display();
+void displayPickingObjects();
+
+void setScene();
 
 #endif
 

editor/src/input.c

@@ -4,6 +4,7 @@
 
 #include "config.h"
 #include "input.h"
+#include "display.h"
 
 void moveCameraPosition(float direction) {
   eyePos += direction;
@@ -46,3 +47,16 @@ void keyboard_special(int key, int x, int y) {
   glutPostRedisplay();
 }
 
+void mouse(int button, int state, int x, int y) {
+  if (button == GLUT_LEFT_BUTTON && state == GLUT_DOWN) {
+    int viewport[4];
+    GLubyte pixel[3];
+
+    displayPickingObjects();
+
+    glGetIntegerv(GL_VIEWPORT, viewport);
+    glReadPixels(x, viewport[3]-y, 1, 1, GL_RGB, GL_UNSIGNED_BYTE, (void*)pixel);
+    printf("%d\n", pixel[2]/8); // Selected LED
+  }
+}
+

editor/src/input.h

@@ -7,5 +7,7 @@ void moveCameraAngle(float angle);
 void keyboard(unsigned char key, int x, int y);
 void keyboard_special(int key, int x, int y);
 
+void mouse(int button, int state, int x, int y);
+
 #endif
 

editor/src/main.c

@@ -33,6 +33,7 @@ int main(int argc, char* argv[]) {
   glutDisplayFunc(display);
   glutKeyboardFunc(keyboard);
   glutSpecialFunc(keyboard_special);
+  glutMouseFunc(mouse);
 
   glClearColor(0.0, 0.0, 0.0, 1.0);
   glShadeModel(GL_SMOOTH);