opengl Getting started with opengl Creating OpenGL 4.1 with C++ and Cocoa
Example
Note: There will be some Objective-c in this example.. We will make a wrapper to C++ in this example, So don't worry to much about it.
First start Xcode and create a project.
And select a Cocoa application
Delete all sources except the Info.plist file.(Your app won't work without it)
Create 4 new source-files: A Objective-c++ file and header (I've called mine MacApp) A C++ class (I've called mine (Application)
In the top left (with the project name) click on it and add linked frameworks and libraries. Add: OpenGL.Framework AppKit.Framework GLKit.Framework
Your project will look probably like this:
NSApplication is the main class you use while creating a MacOS app. It allows you to register windows and catch events.
We want to register (our own) window to the NSApplication. First create in your objective-c++ header a objective-c class that inherits from NSWindow and implements NSApplicationDelegate The NSWindow needs a pointer to the C++ application, A openGL View and a timer for the draw loop
//Mac_App_H
#import <Cocoa/Cocoa.h>
#import "Application.hpp"
#import <memory>
NSApplication* application;
@interface MacApp : NSWindow <NSApplicationDelegate>{
std::shared_ptr<Application> appInstance;
}
@property (nonatomic, retain) NSOpenGLView* glView;
-(void) drawLoop:(NSTimer*) timer;
@end
We call this from the main with
int main(int argc, const char * argv[]) {
MacApp* app;
application = [NSApplication sharedApplication];
[NSApp setActivationPolicy:NSApplicationActivationPolicyRegular];
//create a window with the size of 600 by 600
app = [[MacApp alloc] initWithContentRect:NSMakeRect(0, 0, 600, 600) styleMask:NSTitledWindowMask | NSClosableWindowMask | NSMiniaturizableWindowMask backing:NSBackingStoreBuffered defer:YES];
[application setDelegate:app];
[application run];
}
The implementation of our window is actually quite easy First we declare with synthesise our glview and add a global objective-c boolean when the window should close.
#import "MacApp.h"
@implementation MacApp
@synthesize glView;
BOOL shouldStop = NO;
Now for the constructor. My preference is to use the initWithContentRect.
-(id)initWithContentRect:(NSRect)contentRect styleMask:(NSUInteger)aStyle backing:(NSBackingStoreType)bufferingType defer:(BOOL)flag{
if(self = [super initWithContentRect:contentRect styleMask:aStyle backing:bufferingType defer:flag]){
//sets the title of the window (Declared in Plist)
[self setTitle:[[NSProcessInfo processInfo] processName]];
//This is pretty important.. OS X starts always with a context that only supports openGL 2.1
//This will ditch the classic OpenGL and initialises openGL 4.1
NSOpenGLPixelFormatAttribute pixelFormatAttributes[] ={
NSOpenGLPFAOpenGLProfile, NSOpenGLProfileVersion3_2Core,
NSOpenGLPFAColorSize , 24 ,
NSOpenGLPFAAlphaSize , 8 ,
NSOpenGLPFADoubleBuffer ,
NSOpenGLPFAAccelerated ,
NSOpenGLPFANoRecovery ,
0
};
NSOpenGLPixelFormat* format = [[NSOpenGLPixelFormat alloc]initWithAttributes:pixelFormatAttributes];
//Initialize the view
glView = [[NSOpenGLView alloc]initWithFrame:contentRect pixelFormat:format];
//Set context and attach it to the window
[[glView openGLContext]makeCurrentContext];
//finishing off
[self setContentView:glView];
[glView prepareOpenGL];
[self makeKeyAndOrderFront:self];
[self setAcceptsMouseMovedEvents:YES];
[self makeKeyWindow];
[self setOpaque:YES];
//Start the c++ code
appInstance = std::shared_ptr<Application>(new Application());
}
return self;
}
Alright... now we have actually a runnable app.. You might see a black screen or flickering.
Let's start drawing a awesome triangle.(in c++)
My application header
#ifndef Application_hpp
#define Application_hpp
#include <iostream>
#include <OpenGL/gl3.h>
class Application{
private:
GLuint program;
GLuint vao;
public:
Application();
void update();
~Application();
};
#endif /* Application_hpp */
The implementation:
Application::Application(){
static const char * vs_source[] =
{
"#version 410 core \n"
" \n"
"void main(void) \n"
"{ \n"
" const vec4 vertices[] = vec4[](vec4( 0.25, -0.25, 0.5, 1.0), \n"
" vec4(-0.25, -0.25, 0.5, 1.0), \n"
" vec4( 0.25, 0.25, 0.5, 1.0)); \n"
" \n"
" gl_Position = vertices[gl_VertexID]; \n"
"} \n"
};
static const char * fs_source[] =
{
"#version 410 core \n"
" \n"
"out vec4 color; \n"
" \n"
"void main(void) \n"
"{ \n"
" color = vec4(0.0, 0.8, 1.0, 1.0); \n"
"} \n"
};
program = glCreateProgram();
GLuint fs = glCreateShader(GL_FRAGMENT_SHADER);
glShaderSource(fs, 1, fs_source, NULL);
glCompileShader(fs);
GLuint vs = glCreateShader(GL_VERTEX_SHADER);
glShaderSource(vs, 1, vs_source, NULL);
glCompileShader(vs);
glAttachShader(program, vs);
glAttachShader(program, fs);
glLinkProgram(program);
glGenVertexArrays(1, &vao);
glBindVertexArray(vao);
}
void Application::update(){
static const GLfloat green[] = { 0.0f, 0.25f, 0.0f, 1.0f };
glClearBufferfv(GL_COLOR, 0, green);
glUseProgram(program);
glDrawArrays(GL_TRIANGLES, 0, 3);
}
Application::~Application(){
glDeleteVertexArrays(1, &vao);
glDeleteProgram(program);
}
Now we only need to call update over and over again(if you want something to move) Implement in your objective-c class
-(void) drawLoop:(NSTimer*) timer{
if(shouldStop){
[self close];
return;
}
if([self isVisible]){
appInstance->update();
[glView update];
[[glView openGLContext] flushBuffer];
}
}
And add the this method in the implementation of your objective-c class:
- (void)applicationDidFinishLaunching:(NSNotification *)notification {
[NSTimer scheduledTimerWithTimeInterval:0.000001 target:self selector:@selector(drawLoop:) userInfo:nil repeats:YES];
}
this will call the update function of your c++ class over and over again(each 0.000001 seconds to be precise)
To finish up we close the window when the close button is pressed:
- (BOOL)applicationShouldTerminateAfterLastWindowClosed:(NSApplication *)theApplication{
return YES;
}
- (void)applicationWillTerminate:(NSNotification *)aNotification{
shouldStop = YES;
}
Congratulations, now you have a awesome window with a OpenGL triangle without any third party frameworks.
