Offscreen GraphicsBuffer Example Question

C++ coding using Panda3D
1

Hi,

I’m new to Panda3D. I’d like to implement an offscreen graphics buffer for some custom rendering I’m experimenting with. I’ve read through the rendering documentation. Is there an example (preferably C++ but Python is OK) that shows how to do this?

Cheers,

Chris

2

The Teapot on TV sample program shows how to do this. It is Python but the API is quite similar for C++. If you run into any specific issues, we’ll be happy to help.

3

Thanks for the help.

Here’s what I’d like to do:

  1. Render the scene into an offscreen buffer using colours that are different to those in the main window and using a different camera direction.

  2. Read back some of the pixels from the offscreen buffer.

I need to do this regularly as the app runs but not necessarily for every frame - something like once a second would be ok.

So, the first thing I need to do is create an offscreen output buffer?

Here’s what I’ve tried:

string bufferName(“myBuffer”);
GraphicsOutput* buffer;
buffer = GraphicsEngine::make_buffer(window, bufferName, 0, 100, 100);

When I add this code to the first C++ example in the manual I get the following error:

Panda3D_C++_Test.cpp:21: error: no matching function for call to ‘GraphicsEngine::make_buffer(WindowFramework*&, std::string&, int, int, int)’
/Applications/Panda3D/1.6.2/include/graphicsEngine.I:121: note: candidates are: GraphicsOutput* GraphicsEngine::make_buffer(GraphicsStateGuardian*, const std::string&, int, int, int)
make: *** [test.o] Error 1

How do I get the GraphicsStateGuardian* or is there another way to do this?

4

Pass window->get_graphics_window() as first parameter to make_buffer.

5

I tried what was suggested however I’m still getting an error:

Panda3D_C++_Test.cpp: In function ‘int main(int, char**)’:
Panda3D_C++_Test.cpp:21: error: no matching function for call to ‘GraphicsEngine::make_buffer(GraphicsWindow*, const std::string&, int, int, int)’
/Applications/Panda3D/1.6.2/include/graphicsEngine.I:121: note: candidates are: GraphicsOutput* GraphicsEngine::make_buffer(GraphicsStateGuardian*, const std::string&, int, int, int)
make: *** [test.o] Error 1

BTW, I’m working on OSX however my MacBook only has an Intel GMA 950 graphics processor. I set the renderer to tinydisplay as this was the only one I could get to work. Could this be a problem?

Here’s the full source code I’m using:

#include “pandaFramework.h”
#include “pandaSystem.h”

PandaFramework framework;

int main(int argc, char *argv[]) {

// Open a new window framework
framework.open_framework(argc, argv);

// Set the window title to My Panda3D Window
framework.set_window_title("Panda3D Sound Source Occlusion Test");

// Open the window
WindowFramework *window = framework.open_window();

// Here is room for your own code.
const string bufferName("myBuffer");

GraphicsOutput* buffer; 
buffer = GraphicsEngine::make_buffer(window->get_graphics_window(), bufferName, 0, 100, 100);   

// Do the main loop, equal to run() in python
framework.main_loop();

// Close the window framework
framework.close_framework();

return (0);

}

6

Oh, sorry, I misread. It should be window->get_graphics_window()->get_gsg().

7

I’m still getting errors:

Panda3D_C++_Test.cpp:23: error: cannot call member function ‘GraphicsOutput* GraphicsEngine::make_buffer(GraphicsStateGuardian*, const std::string&, int, int, int)’ without object
make: *** [test.o] Error 1

Here’s the code:

GraphicsWindow* gw = window->get_graphics_window();
GraphicsStateGuardian* gsg = gw->get_gsg();

GraphicsOutput* buffer;
buffer = GraphicsEngine::make_buffer(gsg, bufferName, 0, 100, 100);

8

You’re calling it as if it were a static method. Try something like:

PT(GraphicsWindow) gw = window->get_graphics_window();
PT(GraphicsStateGuardian) gsg = gw->get_gsg();

PT(GraphicsOutput) buffer;
buffer = gsg->get_engine()->make_buffer(gsg, bufferName, 0, 100, 100);