Is this a real concern ? Afterall vector data is a lot less complex than 3d geometry and CPUs nowdays are multicore.

For really smooth and complex animations, yes it is a concern. Performance. If the objective is to draw a static shape or a slow animation, it is not a big problem. Also CPU <-> GPU data transferring is an expensive operation that has to be avoided if possible.

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Actually 2D vector data is more complex. 3D geometry comes already processed to be directly rendered, and it is represented by only two arrays: vertices and indices.

In contrast, 2D vector data is represented by a stream of commands that have to be evaluated.

BTW, we don't have support for real multithreading in Pharo, and we will not have it for a very long time. The closest thing to real multithreading that we are getting in the near term

Don't know about the Opengl backend of Cairo. Igor also once shown me a Spec for vector graphics on OpenGL by Khronos Group.

Well, there is OpenVG designed for mobile platform(Android and iOS). OpenVG is not supported by desktop graphic cards vendors.

The closest thing we have in the desktop world is the NV_path_rendering NVIDIA only extension. At least the paper that describes this extension is really good. The bad thing is that it depends at least partially in the Loop-Blinn algorithm that is patented, if I remember right.

Newest OpenGL versions also come with dynamic tesselation geometry shaders that basically increase the detail of a 3d object the closer a camera gets to it which is similar to vector graphics which is something that could also work as basic via NBOpenGL to bring Athens to 3d side completely bypassing Cairo.��

In first place, not all of the world have at least DX11/OpenGL 4.xx level graphic card. But, it does not matter too much because the hardware tessellation does not help you anything with the main problem.

The biggest problem is that 2D vector paths can be concave, and they can have a hole . The easiest way to support it is by using the stencil buffer, and in my opinion is the method with the better results. In fact, the NV_path_rendering extension is implemented in this way, but directly in the OpenGL driver.

This method renders first the tessellated path with a triangle fan, with the stencil test set to invert the stencil buffer bits. In this way, the stencil buffer holds 1 in the points that are inside of the path, and 0 in the points that are outside of the path.

Then, the bounding box of the path is covered with fill color/gradient, but with the stencil test set to only pass when the stencil buffer value is 1, and to also clear the stencil buffer in the covered region during the process to allow rendering more paths elements.

Each one of the changes to the way the stencil buffer is used involves a state change, which is expensive. I think this is the reason of why NVIDIA implemented their extension directly in the OpenGL.

I know of these problems because I implemented once the stencil method in C++ with OpenGL.

The old opengl Cairo backend worked by triangulating the paths. Triangulation of concave geometry is hard to do, and there some degenerate case in which it produces bad results.

Best regards

Ronie

2014-12-30 16:58 GMT-03:00 kilon alios <kilon.alios@gmail.com>:

Is this a real concern ? Afterall vector data is a lot less complex than 3d geometry and CPUs nowdays are multicore.

Don't know about the Opengl backend of Cairo. Igor also once shown me a Spec for vector graphics on OpenGL by Khronos Group.��

So there are alternatives but as always it will require someone doing the hard work to bring that functionality to Pharo.��

Newest OpenGL versions also come with dynamic tesselation geometry shaders that basically increase the detail of a 3d object the closer a camera gets to it which is similar to vector graphics which is something that could also work as basic via NBOpenGL to bring Athens to 3d side completely bypassing Cairo. ��

On Tue, Dec 30, 2014 at 9:18 PM, Ronie Salgado <roniesalg@gmail.com> wrote:
Athens uses Cairo , Cairo can be used with OpenGL. You can use Cairo to apply a 2d vector graphic as a texture to a 3d polygon. Cairo website shows several examples of this. That means its possible to have 2d vector graphics in 3d space as if its true 3d.
I do not think that is going to work easily with the best performance possible. Cairo could be using OpenGL, but probably in a different OpenGL than the one that is being used for 3d graphics.

In addition, the Cairo OpenGL backend is experimental (http://cairographics.org/OpenGL/) . Currently you have to render into a surface in CPU, then transfer it into GPU and then render the polygon. A naive version using the OpenGL backend is going to have GPU->CPU->GPU roundtrip

If we are using this route, I think that is better to just use the current version of Athens for this. With Athens we can render into a Form, which can be used to populate a Woden/Roassal texture or transferred directly to OpenGL. This has the advantage of not having a explicit dependency in Cairo. I guess that I will make a demo of this later. It should be easy.

I think that a longer term approach could be having a custom renderer, tailored for Athens using OpenGL or maybe OpenCL.

2D vector graphics are really hard. In my opinion they are harder than 3d graphics because of concave self intersecting paths. Stroking a path can be really hard because of thins such as tapering.

The 3D hardware is designed to draw efficiently points, lines and triangles. All of them are simple convex polygon. Most of the 2D vector engines such as Cairo are software renderer, scanliners to be more specific. The old cairo opengl backend had to tessellate the paths

Later I am going to take a better look in Jun. And see how I can integrate with Woden/Woden-Roassal. For what I have seen in the videos, it seems to be using software rendering. Currently I have been working in my internship about volumetric data visualization and the new FFI.

2014-12-30 11:01 GMT-03:00 kilon alios <kilon.alios@gmail.com>:

Athens uses Cairo , Cairo can be used with OpenGL. You can use Cairo to apply a 2d vector graphic as a texture to a 3d polygon. Cairo website shows several examples of this. That means its possible to have 2d vector graphics in 3d space as if its true 3d.��

On Tue, Dec 30, 2014 at 12:10 AM, stepharo <stepharo@free.fr> wrote:
Sven

Jun is a 3D frameworks developed in 1998 in VisualWorks http://aokilab.kyoto-su.ac.jp/jun/index.html
It was quite advanced and this is nice to get more people doing 3d in Pharo.
They are using the back -end developed by ronie and JB and this is cool

Athens is just a canvas and a oo decomposition of the canvas, brush and strokes
nothing related to 3D.
Stef

Le 29/12/14 20:20, Sven Van Caekenberghe a ��crit :

On 29 Dec 2014, at 15:36, stepharo <stepharo@free.fr> wrote:

https://www.youtube.com/watch?v=sH_P5otiWJM&feature=youtu.be

It certainly looks nice, but what is Jun exactly ?