Multiwindow linux gl resource sharing?

Using Cinder
1

Hi,

I encountered an issue when porting an OSX app to Linux. Created a basic test with and Fbo whose color texture should be shared between the two windows, but it isn’t. What is the correct way of doing this? If I remember correctly this has worked before for me on Linux.
Latest Cinder git master with gtx 1080, proprietary driver 375.39, on Fedora 25.

Thanks,
-Gabor

OSX:

multiwindow-osx.jpg1396×1124 71.1 KB

Linux:

multiwindow-linux.png720×579 62.5 KB 

#include "cinder/app/App.h"
#include "cinder/app/RendererGl.h"
#include "cinder/gl/gl.h"

using namespace ci;
using namespace ci::app;

class MultiWindowTestApp : public App
{
 public:
	void setup() override;
	void update() override;

 private:
	app::WindowRef mWindow0;
	app::WindowRef mWindow1;

	void drawWindow( size_t windowId );

	void renderFbo();

	gl::FboRef mFbo;
};

void MultiWindowTestApp::setup()
{
    mFbo = gl::Fbo::create( 1920, 1080 );

	mWindow0 = app::getWindow();
	mWindow0->getSignalDraw().connect( [ & ]() { drawWindow( 0 ); } );

	mWindow1 = createWindow( Window::Format().size( ivec2( 400 ) ) );
	mWindow1->getSignalDraw().connect( [ & ]() { drawWindow( 1 ); } );
}

void MultiWindowTestApp::renderFbo()
{
	gl::ScopedFramebuffer fbo( mFbo );
	gl::ScopedViewport viewport( mFbo->getSize() );
	gl::clear( Color( 1.0f, 0.0f, 0.2f ) );
}

void MultiWindowTestApp::update()
{
	renderFbo();
}

void MultiWindowTestApp::drawWindow( size_t windowId )
{
	gl::viewport( getWindowSize() );
	gl::setMatricesWindow( getWindowSize() );

	gl::clear();
	gl::draw( mFbo->getColorTexture(), getWindowBounds() );
}

CINDER_APP( MultiWindowTestApp, RendererGl )
2

It seems I didn’t remember it right, I had to modify Cinder and pass the first window to glfwCreateWindow before to share the context.

3

This is true.

Unfortunately in GLFW the abstractions make the concept of Window and Context virtually inseparable. The only way to share context in GLFW-land is the way you describe so we would have to figure out a way to allow this, potentially with a Linux-GLFW ifdef clause inside cinder::app::Window::Format which allows one to pass a pointer of the window to share context with.

Probably deserves an issue ticket on its own.

4

Thanks Petros. The way I hacked it in, is that I’m sharing the context of the first window with all other windows automatically in WindowImplLinux. Is it how it works on other platforms, isn’t it?