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Displaying SVG in OpenGL without intermediate raster
(5 answers)
Closed 5 years ago.
Is there a way to load a vector graphics file and then render it using OpenGL? This is a vague question as I don't know much about file formats for vector graphics. I know of SVG, though.
Turning it to raster isn't really helpful as I want to do real time zooming in on the objects.
I see most of the answers are about Qt somehow, even though the original question doesn't mention it. Here's my answer in terms of OpenGL alone (which also benefits greatly from the passage of time, as it could not have been given in 2010):
Since 2011, the state of the art is Mark Kilgard's baby, NV_path_rendering, which is currently only a vendor (Nvidia) extension as you might have guessed already from its name. There are a lot of materials on that:
https://developer.nvidia.com/nv-path-rendering Nvidia hub, but some material on the landing page is not the most up-to-date
http://developer.download.nvidia.com/devzone/devcenter/gamegraphics/files/opengl/gpupathrender.pdf Siggraph 2012 paper
http://on-demand.gputechconf.com/gtc/2014/presentations/S4810-accelerating-vector-graphics-mobile-web.pdf GTC 2014 presentation
http://www.opengl.org/registry/specs/NV/path_rendering.txt official extension doc
NV_path_rendering is now used by Google's Skia library behind the scenes, when available. (Nvidia contributed the code in late 2013 and 2014.)
You can of course load SVGs and such https://www.youtube.com/watch?v=bCrohG6PJQE. They also support the PostScript syntax for paths. You can also mix path rendering with other OpenGL (3D) stuff, as demoed at:
https://www.youtube.com/watch?v=FVYl4o1rgIs
https://www.youtube.com/watch?v=yZBXGLlmg2U
An upstart having even less (or downright no) vendor support or academic glitz is NanoVG, which is currently developed and maintained. (https://github.com/memononen/nanovg) Given the number of 2D libraries over OpenGL that have come and gone over time, you're taking a big bet using something not supported by a major vendor, in my humble opinion.
This isn't an implementation, but very relevant to your question and viewers.
Chapter 25. Rendering Vector Art on the GPU
https://developer.nvidia.com/gpugems/GPUGems3/gpugems3_ch25.html
Let me expand on Greg's answer.
It's true that Qt has a SVG renderer class, QSvgRenderer. Also, any drawing that you do in Qt can be done on any "QPaintDevice", where we're interested in the following "paint devices":
A Qt widget;
In particular, a GL-based Qt widget (QGLWidget);
A Qt image
So, if you decide to use Qt, your options are:
Stop using your current method of setting up the window (and GL context), and start using QGLWidget for all your rendering, including the SVG rendering. This might be a pretty small change, depending on your needs. QGLWidget isn't particularly limiting in its capabilities.
Use QSvgRenderer to render to a QImage, then put the data from that QImage into a GL texture (as you normally would), and render it any way you want (e.g. into a rectangular GL_QUAD). Might have worse performance than the other method but requires the least change to your code.
Wondering what QGLWidget does exactly? Well, when you issue Qt rendering commands to a QGLWidget, they're translated to GL calls for you. And this also happens when the rendering commands are issued by the SVG renderer. So in the end, your SVG is going to end up being rendered via a bunch of GL primitives (lines, polygons, etc).
This has a disadvantage. Different videocards implement OpenGL slightly differently, and Qt does not (and can not) account for all those differences. So, for example, if your user has a cheap on-board Intel videocard, then his videocard doesn't support OpenGL antialiasing, and this means your SVG will also look aliased (jaggy), if you render it directly to a QGLWidget. Going through a QImage avoids such problems.
You can use the QImage method when you're zooming in realtime, too. It just depends on how fast you need it to be. You may need careful optimizations such as reusing the same QImage, and enabling clipping for your QPainter.
Qt has good support for directly rendering SVG images using OpenGL functionality (see the documentation for QSvgRenderer).
I hope that helps.
It has primitives like GL_LINES and GL_LINE_STRIP for drawing lines in space if that's what you mean. Edit: This site has some information: http://www.falloutsoftware.com/tutorials/gl/gl2p5.htm
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I started working at this company that uses an 2D OpenGL implementation to show our system's data (which runs on Windows.) The whole system was built with C++ (using C++Builder 2007). Thing is, all the text they print there are pixelized when you zoom in, which I think happens because the text is a bitmap:
From what I know they use the same font files as Windows does. I asked around here on why this happens and the answer I got is that the guy who implemented it (which doesn't work at the company anymore) said fonts on OpenGL are hard and this was the best he could do or something like it.
My question is: is there any simple and effective way to make the text also a vector (the same way those lines in the picture are?) So when I zoom the camera, which happens a lot, they don't pixelize. I have little knowledge of OpenGL and if you have some guide and/or tutorial related to this to point me towards the right direction I'd be very thankful. Basically any material would be great.
Most of OpenGL text rendering libraries come to this: creating bitmaps for the fonts. This means you are going to have problems with scaling and aliasing unless you do some hacks.
One of the popular hacks is Valve's approach: Chris Green. 2007. "Improved Alpha-Tested Magnification for Vector Textures and Special Effects.". You use signed distance field algo to generate your fonts bitmap which then helps you to smooth the text outlines on scale during rendering. Wikidot has the C++ implementation for Distance field generation.
If you stick to NVidia specific hardware, you can try the NVidia Path extension which allows you to render graphics directly on GPU. Remember, it is a NVidia only thing.
But in general, signed distance field based approach is the smoothest and easiest to implement.
BTW, freetype-gl uses Valve's approach and also the modern pipeline.
You can try freetype-gl its a library for font rendering in OpenGL.
The issue with using fonts in OpenGL is that they are handled inconsistently across platforms, and that they have minimal support. If you're willing to go with a helper library for OpenGL (SDL comes to mind), then this behaviour will likely be wrapped, meaning that you merely need to provide a suitable font file for them to use.
You may try out FTOGL4 , the fonts for OpenGL4
I know GLUT's quadrics, I used it in a few programs when I was in school. Now I'm working on a real world application and I find myself in need of drawing some geometric primitives (cubes, spheres, cylinders), but now I also know that GLUT is a no longer supported and it's last update was in like 2005. So I'm wondering if there's anything other than GLUT's quadrics to draw such geometric shapes. I'm asking if there's anything made before I go ahead and start making my own from vertices arrays.
Yes, you can! You can use the native API of the OS to create a window with OpenGL capabilities.
The advantage of GLUT is that is makes this task easier and is a cross-platform solution.
There are other cross-platform libraries that are more complex to work with but provide the same functionality, like Qt.
NeHe has a huge amount of examples that use several different technologies to accomplish what you are looking for. Check the bottom of the page.
Here is a demo for Windows that creates a window and draws a simple OpenGL triangle inside it. This demo removes all the window frame to give the impression that a triangle is floating on the screen. And here is a similar demo for Linux.
GLUT is just some conveniece framework that came to life way after OpenGL. The problem is not, that GLUT is unmaintained. The problem is, that GLUT was not and never will be meant for serious applications.
Then there's also GLU providing some primitives, but just as GLUT it's merely a companion library. You don't need either.
The way OpenGL works is, that you deliver it arrays of vertex attributes (position, color, normal, texture coordinates, etc.) and tell to draw a set of primitives (points, lines, triangles) from those attributes from a second array of indices referencing into the vertex attribute arrays.
There used to be the immediate mode in versions prior to OpenGL-3 core, but that got depreceated – good riddance. It's only use was for populating display lists which used to have a slight performance advantage if one was using indirect GLX. With VBOs (server (=GPU) side vertex attribute storage) that's no longer an issue.
While GLUT has not been maintained, FreeGLUT has. There are still several alternatives though.
GLFW is a cross-platform windowing system which is easy to get up and running, and also provides the programmer with control of the main application loop.
SFML has support for many languages and also integration capabilities with other windowing schemes, in addition to being cross-platform.
Finally, Qt is another, popular, cross-platform windowing framework.
Now I'm working on a real world application and I find myself in need of drawing some geometric primitives (cubes, spheres, cylinders),
Actually, I don't remember anything except glut that would provide generic primitives. This might have something to do with the fact that those generic primitives are very easy to implement from scratch.
You can use other libraries (libsdl, for example, or Qt) to initialize OpenGL, though.
Most likely if you find generic library for loading meshes (or anything that provides "Mesh" object), then it will have primtives.
is a no longer supported and it's last update was in like 2005
Contrary to popular belief, code doesn't rot and it doesn't get worse with time. No matter how many years ago it was written, if it still works, you can use it.
Also there is FreeGLUT project. Last update: 2012.
By this I mean, does Cairo draw lines, shapes and everything using opengl acelerated primitives or no? and if not, a library that does this?
The OpenGL backend certainly accelerates some functions. But there are many it can't accelerate. The fact that it's written against GL 2.1 (and thus can't use more advanced features of 3.x or 4.x hardware) means that there is a lot that it simply cannot accelerate.
If you are willing to limit yourself to NVIDIA hardware, NVIDIA just came out with the NV_path_rendering extension, which provides a lot of the 2D functionality you would find with Cairo. Indeed, it's possible that you could write a Cairo backend for it. The path rendering extension is only available on GeForce 8xxx hardware and above.
It's nifty in that it's focused on the vertex pipeline. It doesn't do things like gradients or colors or whatever. That's good, because it still allows you the use of a fragment shader. Which means you get to do pretty much whatever you want ;)
Cairo is designed to have a flexible backend for rendering. It can use OpenGL for rendering, though support is still listed as "experimental" at this point. For details, see using cairo with OpenGL.
It can also output to the X Window System, Quartz, Win32, image buffers, PostScript, PDF, and SVG, and more.
This question already has answers here:
Rendering Vector Graphics in OpenGL? [duplicate]
(5 answers)
Closed 5 years ago.
I want to use Vector graphics in an OpenGL game. I want to use vector graphics because they can be scaled cheaply without loss of quality.
Of course, the drawing should be hardware accelerated, so I do not want to draw in software to a texture.
Now I am wondering if a library doing this already exists. Is there a library, that can load some vector graphic format and display it using OpenGL?
I would not bother with anything OpenVG, not even with MonkVG, which is probably the most modern, albeit incomplete implementation. The OpenVG committee has folded in 2011 and most if not all implementations are abandonware or at best legacy software.
Since 2011, the state of the art is Mark Kilgard's baby, NV_path_rendering, which is currently only a vendor (Nvidia) extension as you might have guessed already from its name. There are a lot of materials on that:
https://developer.nvidia.com/nv-path-rendering Nvidia hub, but some material on the landing page is not the most up-to-date
http://developer.download.nvidia.com/devzone/devcenter/gamegraphics/files/opengl/gpupathrender.pdf Siggraph 2012 paper
http://on-demand.gputechconf.com/gtc/2014/presentations/S4810-accelerating-vector-graphics-mobile-web.pdf GTC 2014 presentation
http://www.opengl.org/registry/specs/NV/path_rendering.txt official extension doc
NV_path_rendering is now used by Google's Skia library behind the scenes, when available. (Nvidia contributed the code in late 2013 and 2014.)
And to answer a more specific point raised in the comments, you can mix path rendering with other OpenGL (3D) stuff, as demoed at:
https://www.youtube.com/watch?v=FVYl4o1rgIs
https://www.youtube.com/watch?v=yZBXGLlmg2U
You can of course load SVGs and such https://www.youtube.com/watch?v=bCrohG6PJQE. They also support the PostScript syntax for paths.
An upstart having even less (or downright no) vendor support or academic glitz is NanoVG, which is currently developed and maintained. (https://github.com/memononen/nanovg) Given the number of 2D libraries over OpenGL that have come and gone over time, you're taking a big bet using something not supported by a major vendor, in my humble opinion.
Take a look at OpenVG.
Lots of discussion in this Slashdot post about renderers for SVG. I don't know which of them using OpenGL, if any.
This SO question also has several suggestions, including sauvage which is done in Python. Cairo is also apparently a possibility.
There are several powerful libraries that render SVG without OpenGL. I wonder if it's not really that necessary: maybe drawing lines is already accelerated enough on most systems' graphics cards.
For those not familiar with Core Image, here's a good description of it:
http://developer.apple.com/macosx/coreimage.html
Is there something equivalent to Apple's CoreImage/CoreVideo for Windows? I looked around and found the DirectX/Direct3D stuff, which has all the underlying pieces, but there doesn't appear to be any high level API to work with, unless you're willing to use .NET AND use WPF, neither of which really interest me.
The basic idea would be create/load an image, attach any number of filters that can be chained together, forming a graph, and then render the image to an HDC, using the GPU to do most of the hard work. DirectX/Direct3D has these pieces, but you have to jump through a lot of hoops (or so it appears) to use it.
There are a variety of tools for working with shaders (such as RenderMonkey and FX-Composer), but no direct equivalent to CoreImage.
But stacking up fragment shaders on top of each other is not very hard, so if you don't mind learning OpenGL it would be quite doable to build a framework that applies shaders to an input image and draws the result to an HDC.
Adobe's new Pixel Blender is the closest technology out there. It is cross-platform -- it's part of the Flash 10 runtime, as well as the key pixel-oriented CS4 apps, namely After Effects and (soon) Photoshop. It's unclear, however, how much is currently exposed for embedding in other applications at this point. In the most extreme case it should be possible to embed by embedding a Flash view, but that is more overhead than would obviously be idea.
There is also at least one smaller-scale 3rd party offering: Conduit Pixel Engine. It is commercial, with no licensing price clearly listed, however.
I've now got a solution to this. I've implemented an ImageContext class, a special Image class, and a Filter class that allows similar functionality to Apple's CoreImage. All three use OpenGL (I gave up trying to get this to work on DirectX due to image quality issues, if someone knows DirectX well contact me, because I'd love to have a Dx version) to render an image(s) to a context and use the filters to apply their effects (as HLGL frag shaders). There's a brief write up here:
ImageKit
with a screen shot of an example filter and some sample source code.