I am developing a Qt application that requires visualizations of very large data sets. I was hoping to use Qt's 3D graphing functionality (Q3DBars) to make the data more easily understood. However, I am having difficulty getting a reasonable framerate.
I have done the below in hopes that the framerate would improve. No effect.
bars.setReflection(false);
bars.setReflectivity(false);
bars.setOptimizationHints(...::QAbstract3DGraph::OptimizationHint::OptimizationStatic);
bars.setShadowQuality(QAbstract3DGraph::ShadowQuality::ShadowQualityNone);
bars.setSurfaceType(QSurface::OpenGLSurface);
I have a GTX1080 and windows records 40% GPU usage as I rotate the graph. However, the CPU is loaded significantly during the same rotation.
What can be done to further offload work to the GPU and/or optimize the rendering?
After playing with the other 3D graph classes, I have discovered that Q3DSurface runs smoothly with the same data set. I am unsure what the specific difference is but I suspect the surface is rendered in a vastly different way. Initially, the image looked unclear.
However, after disabling the wireframe the image became very clear.
Related
I'm working on a data visualisation application where I need to draw about 20 different time series overlayed in 2D, each consisting of a few million data points. I need to be able to zoom and pan the data left and right to look at it and need to be able to place cursors on the data for measuring time intervals and to inspect data points. It's very important that when zoomed out all the way, I can easily spot outliers in the data and zoom in to look at them. So averaging the data can be problematic.
I have a naive implementation using a standard GUI framework on linux which is way too slow to be practical. I'm thinking of using OpenGL instead (testing on a Radeon RX480 GPU), with orthogonal projection. I searched around and it seems VBOs to draw line strips might work, but I have no idea if this is the best solution (would give me the best frame rate).
What is the best way to send data sets consisting of millions of vertices to the GPU, assuming the data does not change, and will be redrawn each time the user interacts with it (pan/zoom/click on it)?
In modern OpenGL (versions 3/4 core profile) VBOs are the standard way to transfer geometric / non-image data to the GPU, so yes you will almost certainly end up using VBOs.
Alternatives would be uniform buffers, or texture buffer objects, but for the application you're describing I can't see any performance advantage in using them - might even be worse - and it would complicate the code.
The single biggest speedup will come from having all the data points stored on the GPU instead of being copied over each frame as a 2D GUI might be doing. So do the simplest thing that works and then worry about speed.
If you are new to OpenGL, I recommend the book "OpenGL SuperBible" 6th or 7th edition. There are many good online OpenGL guides and references, just make sure you avoid the older ones written for OpenGL 1/2.
Hope this helps.
I'm writing a 2D platformer game using SDL with C++. However I have encountered a huge issue involving scaling to resolution. I want the the game to look nice in full HD so all the images for the game have been created so that the natural resolution of the game is 1920x1080. However I want the game to scale down to the correct resolution if someone is using a smaller resolution, or to scale larger if someone is using a larger resolution.
The problem is I haven't been able to find an efficient way to do this.I started by using the SDL_gfx library to pre-scale all images but this doesn't work as it creates a lot of off-by-one errors, where one pixel was being lost. And since my animations are contained in one image when the animation would play the animation would slightly move up or down each frame.
Then after some looking round I have tried using opengl to handle the scaling. Currently my program draws all the images to a SDL_Surface that is 1920x1080. It then converts this surface to a opengl texture, scales this texture to the screen resolution, then draws the texture. This works fine visually but the problem is that its not efficient at all. Currently I am getting a max fps of 18 :(
So my question is does anyone know of an efficient way to scale the SDL display to the screen resolution?
It's inefficient because OpenGL was not designed to work that way. Main performance problems with current design:
First problem: You're software rasterizing with SDL. Sorry, but no matter what you do with this configuration, that will be a bottleneck. At a resolution of 1920x1080, you have 2,073,600 pixels to color. Assuming it takes you 10 clock cycles to shade each 4-channel pixel, on a 2GHz processor you're running a maximum of 96.4 fps. That doesn't sound bad, except you probably can't shade pixels that fast, and you still haven't done AI, user input, game mechanics, sound, physics, and everything else, and you're probably drawing over some pixels at least once anyway. SDL_gfx may be quick, but for large resolutions, the CPU is just fundamentally overtasked.
Second problem: Each frame, you're copying data across the graphics bus to the GPU. This is the slowest thing you can possibly do graphics-wise. Image data is probably the worst of that, because there's typically so much of it. Basically, each frame you're telling the GPU to copy two million some pixels from RAM to VRAM. According to Wikipedia, you can expect, for 2,073,600 pixels at 4 bytes each, no more than 258.9 fps, which again doesn't sound bad until you remember everything else you need to do.
My recommendation: switch your application completely to OpenGL. This removes the need to render to a texture and copy to the screen--just render directly to the screen! Also, scaling is handled automatically by your view matrix (glOrtho/gluOrtho2D for 2D), so you don't have to care about the scaling issue at all--your viewport will just show everything at the same scale. This is the ideal solution to your problem.
Now, it comes with the one major drawback that you have to recode everything with OpenGL draw commands (which is work, but not too hard, especially in the long run). Short of that, you can try the following ideas to improve speed:
PBOs. Pixel buffer objects can be used to address problem two by making texture loading/copying asynchronous.
Multithread your rendering. Most CPUs have at least two cores and on newer chips two register states can be saved for a single core (Hyperthreading). You're essentially duplicating how the GPU solves the rendering problem (have a lot of threads going). I'm not sure how thread safe SDL_gfx is, but I bet that something could be worked out, especially if you're only working on different parts of the image at the same time.
Make sure you pay attention to what place your draw surface is in SDL. It should probably be SDL_SWSURFACE (because you're drawing on the CPU).
Remove VSync. This can improve performance, even if you're not running at 60Hz
Make sure you're drawing your original texture--DO NOT scale it up or down to a new one. Draw it at a different size, and let the rasterizer do the work!
Sporadically update: Only update half the image at a time. This will probably close to double your "framerate", and it's (usually) not noticeable.
Similarly, only update the changing parts of the image.
Hope this helps.
I would like to make a basic real time CPU ray tracer in C++ (mainly for learning proposes). This tutorial was great for making a basic ray tracer. But what would be the best solution to draw this on the screen in real time? I'm not asking on how to optimize the ray tracing-part, just the painting part so that it would paint on the screen and not in a file.
I'm developing on/for windows.
You could check out this Code Project article on the basic paint mechanism using Win32API
Update: OP wants fast drawing, which the Win32API does not provide. The OP needs this so that they can measure speedup of the ray-tracing algorithm during optimization process. Other possibilities for drawing are: DirectX, XNA, Allegro, OpenGL.
I'm professionally working on a realtime CPU raytracer, and from what I saw with 2 years of work there, the GPU part to display image won't be the bottleneck, the bottleneck if you reach it will be the speed of your RAM, I don't think the drawing technology will make any significant difference.
As an example, we are using clustering (one CPU is not enough :p), we were able to render 100-200fps at 1920x1080 when looking the sky but the bottleneck was not the display part, it was the network...
EDIT: We are using OpenGL for the display.
When you are doing a CPU raytracer you are not gonna do printPixelToGPU() but you will write to your RAM and then send it to the GPU once the image is finished. Doing printPixelToGPU() would probably cause an big overhead and it is (in my opinion) a really bad design choice.
It looks like premature optimization. But if you are still concerned about that, just do a bench of how many RAM textures to GPU transfer you can do with OpenGL, directX..., and print the average framerate. You will probably see that the framerate will be really really high, so you will certainly never reach that "bottleneck" unless you are using SDRAM or a really poor GPU.
Nowadays we have pretty advanced tools to iron out rendering, allowing to see the different stages, time taken by draw calls, etc. But without them the graphics pipeline is quite a black box when it comes to understand what is happening inside.
Suppose for some reason you have no such tool, or a very limited one. How would you measure anyway what is taking time in your rendering?
I am aware of tricks like discarding draw calls to see the CPU time, setting a 1x1 viewport to see the cost of geometry, using a dumb fragment shader to highlight the fillrate... They are useful already but only give a rough idea of what is going on, and tell nothing about the level of parallelism.
Also, getting the time spent in each stage per draw call seem to be difficult, especially when taking into account the lack of precision due to the noise when measuring.
What tricks do you use when your backpack is almost empty and you still have to profile your rendering? What is your personal Swiss army knife consisting in?
Frame time rendering time
Absolute time spent for small code/stage/etc. is not that relevant as GPU driver optimization/batching/parallelism/version makes it nearly impossible to have precise code measure without GPU counters. (which you can get if you use with vendors libs)
What you can measure easily is each single code change impact. You'll only get relative impact, and it's what you really need anyway. And that just using frame rendering time.
Ideally you should aim be able can edit shader or pipeline code during runtime, and have a direct way to check impact over a whole typical scene, like just comparing graphs between several code path. (beware of static scenes, otherwise you'll end with highly optimized static views, but poor dynamic scenes performance)
Here's the swiss army knife list:
scene states loader
scene recorder (camera paths/add-remove entities,texture, mesh, fake input, etc.) using scene states.
scene states saver
scene frame time logger (not just final average but each frame rendering time)
on-the-fly shader code reload
on-the-fly codepath switch
frame time log reader+graphs+statistic framework
Note that scene state load/save/record are handy for a lot of other things, from debugging to undo/redo to on-the-fly reload, not to mention savegames.
Add a screenshot taker + image diff, and you can unit test graphic code too.
If you can, add that to your CI server so that huge code impact doesn't go unnoticed. (helps also artists when they check-in their assets, without evaluating rendering impact)
A must read on that related CI graphic test work is there : http://aras-p.info/blog/2011/06/17/testing-graphics-code-4-years-later/
Note: I'm responding to the question: "Profiling a graphics rendering with a profiler", since that something I was looking for ;)
I'm working mostly on Mac, and I'm using multiple tools:
gDebugger version 5.8 is available on Windows and Mac (this tool has been bought by AMD, the v6 version is Windows only). It gives you statistics about state changes, texture usage, draw calls, etc. It's also usefull to debug texture mapping, and see how your scene is drawn, step by step.
PVRUniSCoEditor it's a shader editor. It compiles on the fly and give you precious details about estimated cycles and registers usage.
Instruments (from XCode Utilities, OSX only), it gets informations from the OpenGL driver, it's great to find bottleneck since you can track what part of the GPU is used at 100% (tiler, renderer, texture unit, etc...)
Adreno Profiler a Windows tool to profile Adreno-based mobile devices. (Very good tool if you work on Android apps ;))
What's your trick about the "dumb fragment shader to highlight the fillrate" ? (drawing a plain color ? or something more advanced ?)
If we want to make an application like MS Paint, should we use OpenGL for render graphics?
I want to mention about performance if using traditional GDI vs. OpenGL.
And if there are exist some better libs for this purpose, please see me one.
GDI, X11, OpenGL... are rendering APIs, i.e. you usually don't use them for image manipulation (you can do this, but it requires some precautions).
In a drawing application like MS Paint, if it's pixel based, you'll normally manipulate some picture buffer with customary code, or a special image manipulation library, then send the full buffer to the rendering API.
If your data model consists of strokes and individual shapes, i.e. vector graphics, then OpenGL makes a quite good backend. However it may be worth looking into some other API for vector graphics, like OpenVG (which in its current implementations sits on top of OpenGL, but native implementations operating directly on the GPU may come).
In your usage scenario you'll not run into any performance problems on current computers, so don't choose your API from that criteria. OpenGL is definitely faster than GDI when it comes to texturing, alpha blending, etc. However depending on system and GPU pure GDI may outperform OpenGL for so simple things like drawing an arc or filling a complex self intersecting polygon with complex winding rules.
There is no good reason not to use OpenGL for this. Except maybe if you have years of experience with GDI but don't know a single thing about OpenGL.
On the other hand, OpenGL may very well be superior in many cases. Compositing layers or adjusting hue/saturation/brightness/contrast in a GLSL shader will be several orders of magnitude faster (in fact, pretty much "instantly") if there is a reasonably new card in the computer. Stroking a freedraw path with a "fuzzy" pen (i.e. blending a sprite with alpha transparency over and over again) will be orders of magnitude faster. On images with somewhat reasonable dimensions, most filter kernels should run close to realtime. Rescaling with bilinear filtering runs in hardware.
Such things won't matter on a 512x512 image, as pretty much everything is instantaneous at such resolutions, but on a typical 4096x3072 (or larger) image from your digital camera, it may be very noticeable, especially if you have 4-6 layers.