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.
Related
I have used OpenGL pretty exclusively for all my rendering, to the point that I'm unaware of any other way to write pixels to a window unfortunately.
This is a problem because my current project is a work tool that emulates an LCD display (pixel perfect, 2D, very few pixels are touched each frame, all 'drawing' can be done with memcpy() to a pixel buffer) and I feel that OpenGL might be too heavy for this, but I could absolutely be wrong in that assumption.
My goal is to borrow as little CPU time as possible. What's the best way to draw pixels to a window, in this limited way, on a modern typical machine running windows 10 circa 2019? Is OpenGL suited for this type of rendering, or should I adopt another rendering method in this case? And if so, what would that method be?
edit:
I should also mention, OpenGL can be used right away for me. If rendering textured triangles with an optimal setup is the fastest method, then I can already do that. Anything that just acts as an API over OpenGL or DirectX will likely be worse in my case.
edit2:
After some research, and thanks to the comments, I think I may just use OpenGL with Pixel Buffer Objects to optimize pixel uploads and keep rendering inexpensive.
I'm writing a 2D, sprite-based game and I'm having a hard time with making collision detection. First of all, I am well aware of other methods and in fact I'm using Box2D's quadtree queries to filter out non-overlapping sprites. So pixel-perfect detection would be used only on sprites that were found to overlap and would be used only a few times per frame. The sprites are rotating but not scaling.
The problem is I need it done with pixels because the sprites can change over time and making and using e.g. Box2D's geometric shapes for approximate the bitmap will get really complicated.
I did some research and found out these methods are possible in OpenGL in order to check if any pixels with non-zero alpha channel overlap:
1) Rendering sprites to a texture/buffer with e.g. 50% alpha and proper blending function, copying the result to RAM and checking if there's any pixel with alpha greater with e.g. 80%.
This method is simple but as I checked copying back is extremely slow.
2) Using OpenGL's occlusion query.
From what I found out on the net occlusion queries can be tricky (plus sometimes you need to wait until the next frame to get the result) and buggy on some graphic cards. The fact such queries don't produce results immediately is a deal breaker because of how the game is designed to work.
3) Shaders and atomic counters.
I'm not sure if it would work but it seems that using a fragment shader when rendering a second sprite that would increase an atomic counter each time it overwrites something and then checking the counter's value on the CPU side could be a solution. The only problem is that atomic counters are pretty new and 2,3-years old machines may not support them.
Is there something I missed? Or should I just forgot about using GPU and write my own renderer just for collision detection on CPU?
Atomic Counters is an appropriate way to do this on the GPU. Since you're going to be checking many many pixels, you might as well do this in parallel. The big performance question here is asynchronously reading it back, but this depends on how you make your engine of course.
With OpenGL 4.2 you can use atomic counters. Check if your graphics card supports this, it's quite possible it does, you should check this.
I'm trying to do a little game in 2D to learn how to do it and improve my programming skills. I programme the game using C++/C and OpenGL 3.0 with GLUT.
I so confused with some important concepts about animations and scenario refresh.
It's a good practice load all the textures only when the level begins ?
I choose a fps rate to 40 fps, should i redraw all the scenario and the agents in every frame or only the modifications ?
In an agent animation should i redraw all the entire agent or only the parts which changes from the past ?
If some part of the scene changes (one wall or something similar is destroyed) should i need to redraw all the entire scene or only the part which changes ?
Now my "game" works with a framerate of 40fps but the game has a flickering effect that looks really weird.
Yes, creating and deleting textures/buffers every frame is a huge waste.
It's almost always cheaper to just redraw the entire scene. GPUs are built to do this, it's very fast.
Reading the framebuffer from VRAM back to regular RAM and calculating the difference is going to be much slower, especially since OpenGL doesn't keep track of your "objects", it just takes a triangle at a time, rasterizes it, then forgets about it.
Depends on how you define the animation. If you're talking about sprite-like animation, where each frame is a separate image, then it's cheapest to just refer to the new texture and redraw.
If you've got a texture atlas, update the texture coordinates and redraw, and if you're using shaders (you pretty much have to if you want to be OpenGL 3.0), you might be able to get away with a uniform that offsets texture coordinates.
Yeah, as I said before, the hardware is built to clear the screen and redraw everything.
And for a framerate, you should be using the monitor's refresh rate to avoid vertical tearing. Pretty much all monitors now are 60Hz, so 60fps is the most common "target" framerate.
Choose either 30 or 60 fps as most modern monitors refresh in 60 Hz rate. So you have either 2 or 1 rendered frame per "monitor frame". This should reduce flickering effects. (I'm not 100% sure if you mean this with "flash effect".)
Regarding all other questions (which sound pretty much the same): In OpenGL rendering, redrawing everything is pretty common, as in most games almost the entire screen changes in every frame, for example if you're moving around. You could do a partial screen update, but it's very uncommon and more expensive on the CPU side, as you have to compute which parts to draw instead of just "draw everything".
Yes
2-4. Yes - Hopefully this help you understand why you must...
Imagine you have 2 pieces of paper. The first paper you draw a stick man standing still, and show that to somebody.
The second paper while the user is looking at that paper you draw the same thing again but this time you move the arm a little bit.
Now you show them the second paper, as they look at the second paper you clear the first paper and draw the man moving his arm a little bit more.
This is pretty much how it works and is the reason you must always render the whole image regardless if nothing has changed.
I'm building a cocos2d game where I use two background sprites, actually one is a sprite, the other one is a CCMask that is used to make holes into the other background, but the performance problem is the same even when using 2 regular background sprites on top of each other.
When I use one background sprite, my FPS is around 60 all the time, when I use two background sprites the FPS drops to 30 every time. I've googled around, tried different solutions including reading sprites from a sprite frame cash instead of from a file, unfortunately the result is the same.
I just can't figure out why this is happening. Does any one here have any idea why this is happening and how to get around it?
On older devices (1st & 2nd generation, ie iPhone 3G) this can easily happen since they have terrible fillrates.
If possible try to SpriteBatch the two background images. You need to add both to a texture atlas, for example with TexturePacker. Sprite batching is particularly effective if the sprites are large.
Also, just in case: don't test performance in the Simulator. Simulator performance has no relation to actual device performance whatsoever.
How can we run a OpenGL applications (say a games) in higher frame rate like 500 - 800 FPS ?
For a example AOE 2 is running with more than 700 FPS (I know it is about DirectX). Eventhough I just clear buffers and swap buffers within the game loop, I can only get about 200 (max) FPS. I know that FPS isn't a good messurenment (and also depend on the hardware), but I feel I missed some concepts in OpenGL. Did I ? Pls anyone can give me a hint ?
I'm getting roughly 5.600 FPS with an empty display loop (GeForce 260 GTX, 1920x1080). Adding glClear lowers it to 4.000 FPS which is still way over 200...
A simple graphics engine (AoE2 style) should run at about 100-200 FPS (GeForce 8 or similar). Probably more if it's multi-threaded and fully optimized.
I don't know what exactly you do in your loop or what hardware that is running on, but 200 FPS sounds like you are doing something else besides drawing nothing (sleep? game logic stuff? greedy framework? Aero?). The swapbuffer function should not take 5ms even if both framebuffers have to be copied. You can use a profile to check where the most CPU time is spent (timing results from gl* functions are mostly useless though)
If you are doing something with OpenGL (drawing stuff, creating textures, etc.) there is a nice extension to measure times called GL_EXT_timer_query.
Some general optimization tips:
don't use immediate mode (glBegin/glEnd), use VBO and/or display lists+vertex arrays instead
use some culling technique to remove objects outside your view (opengl would have to cull every polygon separately)
try minimizing state changes, especially changing the bound texture or vertex buffer
AOE 2 is a DirectDraw application, not Direct3D. There is no way to compare OpenGL and DirectDraw.
Also, check the method you're using for swapping buffers. In Direct3D there are flip method, copy method, and discard method. The best one is discard, which means that you don't care about previous contents in the buffer, and allow the driver to manage them efficiently.
One of the things you seem to miss (judging from your answer/comments, so correct me if I'm wrong) is that you need to determine what to render.
For example as you said you have multiple layers and such, well the first thing you need to do is not render anything that is off screen (which is possible and is sometimes done). What you should also do is not render things that you are certain are not visible, for example if some area of the top layer is not transparent (or filled up) you should not render the layers below it.
In general what I'm trying to say is that it is in most cases better to eliminate invisible things in the logic than to render all things and just let the things on top end up in the rendered image.
If your textures are small, try to combine them in one bigger texture and address them via texture coordinates. That will save you a lot of state changes. If your textures are e.g. 128x128, you can put 16 of them in one 512x512 texture, bringing your texture related state changes down by a factor of 16.