View Full Version : Displaying Large Objects into NSOpenGLView

Aug 27, 2008, 01:58 PM
Well, as you may recall from a previews thread, I am building a .obj file loader. The question I have concerns general OpenGL, so it doesn't require of me to show much code, or from you to know about .obj files. I succeeded in making the loader, and I also succeeded in displaying that object on screen. Materials are also used. (I hope I can implement textures into the next few days...).

I have a problem, though. I have made an application which loads and displays a model. However, as you imagine, the dimensions of each model are completely different. One model could have vertices that have coordinates like those:

x: 1000 y: 8673 z: 9344

Other models may have vertices like those:

x: 9,34 y:7,34 z: 9,44

My problem is that I can't think of any good way of resizing the view each time I load a new model to something that produces a viewable result. My display code so far is the following:

MyOpenGLView.h code:

#import <Cocoa/Cocoa.h>
#import "ObjLoaders.h"
#include <iostream>
#include "General.h"
#include <GLUT/GLUT.h>
using namespace std;

#define FILENAME "lightcycle-low.obj"
#define FILENAME2 "lightcycle-low.txt"
#define FILENAME3 "Cube.obj"
#define FILENAME4 "Cone.obj"
#define FILENAME5 "test/lightcycle-high.obj"
#define FILENAME6 "Bau2.obj"

#define UPDATE_SECONDS 1.0f/200
#define STEP_SIZE 0.5f

@interface MyOpenGLView : NSOpenGLView {

float yRot;
float xRot;
float standardRotationDegrees;

float upAndDownTranslation;
float leftAndRightTranslation;
float nearAndFarTrasnlation;
NSTimer *timer;

- (void)rotate:(float)degrees;

- (IBAction)rotateUp:(id)sender;
- (IBAction)rotateDown:(id)sender;
- (IBAction)rotateLeft:(id)sender;
- (IBAction)rotateRight:(id)sender;
- (IBAction)moveCameraLeft:(id)sender;
- (IBAction)moveCameraRight:(id)sender;
- (IBAction)moveCameraUp:(id)sender;
- (IBAction)moveCameraDown:(id)sender;
- (IBAction)moveCameraForward:(id)sender;
- (IBAction)moveCameraBackwards:(id)sender;

- (IBAction)loadOBJFile:(id)sender;

MyOpenGLView.mm code:

#import "MyOpenGLView.h"

OBJModel model;

@implementation MyOpenGLView

- (void) heartbeat
[self rotate:standardRotationDegrees];
if(![[NSApplication sharedApplication] isHidden])
[self setNeedsDisplay:YES];
//[self rotateLeft:self];

- (void)prepareOpenGL
standardRotationDegrees = 0.3f;
timer = [NSTimer scheduledTimerWithTimeInterval:(UPDATE_SECONDS) target:self selector:@selector(heartbeat) userInfo:nil repeats:YES];
[timer retain];

//[[NSRunLoop currentRunLoop] addTimer: timer forMode: NSDefaultRunLoopMode];
//[[NSRunLoop currentRunLoop] addTimer: timer forMode: NSEventTrackingRunLoopMode];

NSLog(@"preparing openGL...");
glClearColor(0.0f, 0.0f, 0.0f, 1.0f );



yRot = 0.0f;
xRot = 0.0;;
upAndDownTranslation = 0.0f;
leftAndRightTranslation = 0.0f;
nearAndFarTrasnlation = 0.0f;

//GLfloat lightpos[4] = {0.0f, 0.2f, -1.0, 1.0f};
GLfloat lightpos[4] = {2.0f, 2.0f, 2.0, 1.0f};
glLightfv(GL_LIGHT0, GL_POSITION, lightpos);


- (void)reshape
[[self openGLContext]makeCurrentContext];
NSRect bounds = [self bounds];
//NSLog(@"reshaping: %f, %f", NSWidth(bounds), NSHeight(bounds));
glViewport(0, 0, NSWidth(bounds), NSHeight(bounds));
gluPerspective(45, NSWidth(bounds)/NSHeight(bounds), 0.1f, 1000.0f);
// glOrtho(-20, 20, -20, 20, -100, 100);
[NSOpenGLContext clearCurrentContext];


- (void)drawRect:(NSRect)rect {


//glTranslatef(0.0f, 0.0f, -20.0f);

gluLookAt(0, 0, nearAndFarTrasnlation, 0, 0, 0, 0, 1, 0);
glTranslatef(leftAndRightTranslation, 0, 0);
glRotatef(xRot, 1.0f, 0.0f, 0.0f);
glRotatef(yRot, 0.0f, 0.0f, 1.0f);

//draw the model
for (int i=0; i<model.numTriangles(); i++) {

[[self openGLContext]flushBuffer];

#pragma mark -
#pragma mark Moving The Camera
- (void)rotate:(float)degrees
yRot = yRot - degrees;
- (IBAction)rotateUp:(id)sender
xRot-= 5.0f;
if(xRot < 0.1f)
xRot = 359.9;
[self setNeedsDisplay:YES];
- (IBAction)rotateDown:(id)sender
xRot += 5.0f;
if(xRot > 359.9f)
xRot = 0.0f;
[self setNeedsDisplay:YES];
- (IBAction)rotateLeft:(id)sender
yRot -= 5.0f;
if(yRot < 0.1f)
yRot = 359.9;
[self setNeedsDisplay:YES];
- (IBAction)rotateRight:(id)sender
yRot += 5.0f;
if(yRot > 359.9f)
yRot = 0.0f;
[self setNeedsDisplay:YES];

if(standardRotationDegrees > 0.0f)
standardRotationDegrees = 0.0f;

- (IBAction)moveCameraLeft:(id)sender
leftAndRightTranslation -= STEP_SIZE;
[self setNeedsDisplay:YES];
- (IBAction)moveCameraRight:(id)sender
leftAndRightTranslation += STEP_SIZE;
[self setNeedsDisplay:YES];
- (IBAction)moveCameraUp:(id)sender

- (IBAction)moveCameraDown:(id)sender

- (IBAction)moveCameraForward:(id)sender
nearAndFarTrasnlation += STEP_SIZE;
[self setNeedsDisplay:YES];
- (IBAction)moveCameraBackwards:(id)sender
if(nearAndFarTrasnlation < 0)
nearAndFarTrasnlation = 0;
nearAndFarTrasnlation -= STEP_SIZE;
[self setNeedsDisplay:YES];

- (IBAction)loadOBJFile:(id)sender
NSOpenPanel *openPanel = [NSOpenPanel openPanel];
[openPanel setCanChooseDirectories:NO];
[openPanel setCanChooseFiles:YES];
[openPanel setAllowsMultipleSelection:NO];
[openPanel setAllowedFileTypes:[NSArray arrayWithObject:@".obj"]];
if ([openPanel runModalForDirectory:NSHomeDirectory() file:nil] == NSOKButton) {
[[NSFileManager defaultManager]changeCurrentDirectoryPath:[[openPanel filename]stringByDeletingLastPathComponent]];
model.loadOBJFile([[[openPanel filename]stringByStandardizingPath]cStringUsingEncoding:NSUTF8StringEncoding]);

- (void) dealloc
if(timer != nil)
[timer release];
[super dealloc];


As you can see, I have used gluPerspective() with gluLookAt(). Although some models are displayed correctly, I have a model that has vertices like x:300.0 y:20.0 z:1000.0. That model is not displayed at all. Therefore, I need a way to resize the view to something that can hold objects of any size each time I load a new model.

Can you recommend any way of coping with that problem?

Aug 27, 2008, 02:40 PM
Rather than scale the view, I would be tempted to scale the model when you draw it, ie just push a glScale on the model view matrix before drawing it. You could work out the scaling factor from the vertex bounds when you load the model.

b e n