I'm working on someone else's game and am not familiar with SDL or Pascal. What I am trying to do is upgrade the game graphics from 8 bits to 32 bits. So far it is going well, except for the following procedure:
SDL_SetAlpha( Spr^.Img , SDL_SRCAlpha , Alpha_Level );
DrawAnimImage( Spr^.Img , Spr^.W , Spr^.H , Frame , MyDest );
SDL_SetAlpha( Spr^.Img , SDL_SRCAlpha , SDL_Alpha_Opaque );
This code is supposed to change the opacity of a sprite to 50% when your character walks near it. It works well with 8 and probably 24 bit images, but not with 32 bit images. How can I rewrite this code to handle 32 bit images with alpha channels?
This old blog article sort of describes what I need to do, but I am a noob and don't understand all of it.
http://www.sdltutorials.com/the-ins-and-outs-and-overlays-of-alpha-blending
It mentions a library called Sprig. Is this my only choice on how to proceed? How do I use it? Does it work with Pascal programs?
Thanks.
Related
Im making a game in Rust(Im a beginner) for my son and am somehow struggling with platforms - specifically modifying their length. I can get the platforms if i use certain numbers but if i try to modify the platform width I run into problems.
If i use the const PLATFORM_WIDTH=400 then everything works fine (i seemingly can make any number of them and it all works), but I don't want to have platforms of a fixed width (length), I want each platform to be of variable width. If I try to make the platform width say 100.0 then it is rendered correctly but I can walk over empty space as if there was a platform there. If I make them greater than 400 they are rendered but the sprite will fall through solid floor at some points.
Really don't know where Im going wrong and this annoying issue is preventing me from making progress on my game.
Id really appreciate if someone could take a look at my code and tell me where im going wrong.
My code is here:
https://github.com/country-bumpkin-software/rusty-miner/blob/main/src/main.rs
Also can someone explain to me why the Rect function seems to take negative numbers for the x, y coords?
The problem is that you sometimes use the width from the platform struct (e.g. when checking for intersections on line 264) and sometimes use the PLATFORM_WIDTH and PLATFORM_WIDTH_HALF constants (e.g. when drawing the platform on line 346).
I followed the Lighting tutorial on learnopenGL, modifying some of the code to work in a 2D game engine. Everything was looking great and my team got our game done and the lights were quite simple for our designers to use. However we ran into a rare bug. as shown here: https://www.youtube.com/watch?v=to0mMP5I0cs one team member was able to recreate the bug by switching his Nvidia settings to use the "High Performance Processor" as opposed to "Integrated Graphics". Otherwise everything renders properly. The bug doesn't appear when there are no lights and everything is rendered in its full color. We have gone through alot of Ideas already but they haven't worked and now I am at a loss. Does anyone have any ideas about what is going on?
Always make sure you initialize your variables. Apparently some cards and drivers automatically initialize vec3 to (0,0,0), but others don't. That was what was going on here. Garbage values causing different colors at each fragment. By Initializing my resulting color vec3 to (0,0,0) at the beginning the problem is fixed.
Disclaimer: I am not an Objective C programmer, but rather collaborate with and manage such a research project, hence my question may be phrased somewhat naively. However, after many discussions with various experts I am assured that this question is relevant so I turn to you as I would greatly appreciate your input.
We need to resize a UIWebView at the Core Animation level. This is a given fact that cannot be altered and which we don't need to discuss here. Just simply resizing the UIWebView itself is not a possibility for this application. Here's the crux:
We load a UIWebView of a certain geometry, let's say 256 x 256 pixel, and then we resize it with Core Animation. Let's say the new target size will be 1024 x 512 pixel. We manage to easily make the UIWebView fit nicely into the new 512 wide space. The problem, however, is that it keeps it's original proportions so that the new UIWebView now covers only half of the target area, i.e. 512 x 512 pixel. This is not unexpected, however, we need the UIWebView to reveal more of its content after such a transform, i.e. to become longer, as to fill the space. We're pretty stuck as we don't really have any other alternative. Once you start thinking about this problem and trying various scenarios you'll find that this is not trivial. If you have any ideas as to how we could resolve / work-around this problem, that would be great!
Let me know - All the best,
Michael
Try [webView.scrollView setZoomScale:1f] after resizing.
"Super Meat Boy" is a difficult platformer that recently came out for PC, requiring exceptional control and pixel-perfect jumping. The physics code in the game is dependent on the framerate, which is locked to 60fps; this means that if your computer can't run the game at full speed, the physics will go insane, causing (among other things) your character to run slower and fall through the ground. Furthermore, if vsync is off, the game runs extremely fast.
Could those experienced with 2D game programming help explain why the game was coded this way? Wouldn't a physics loop running at a constant rate be a better solution? (Actually, I think a physics loop is used for parts of the game, since some of the entities continue to move normally regardless of the framerate. Your character, on the other hand, runs exactly [fps/60] as fast.)
What bothers me about this implementation is the loss of abstraction between the game engine and the graphics rendering, which depends on system-specific things like the monitor, graphics card, and CPU. If, for whatever reason, your computer can't handle vsync, or can't run the game at exactly 60fps, it'll break spectacularly. Why should the rendering step in any way influence the physics calculations? (Most games nowadays would either slow down the game or skip frames.) On the other hand, I understand that old-school platformers on the NES and SNES depended on a fixed framerate for much of their control and physics. Why is this, and would it be possible to create a patformer in that vein without having the framerate dependency? Is there necessarily a loss of precision if you separate the graphics rendering from the rest of the engine?
Thank you, and sorry if the question was confusing.
There are no reasons why physics should depend on the framerate and this is clearly a bad design.
I've once tried to understand why people do this. I did a code review for a game written by another team in the company, and I didn't see it from the beginning but they used a lot of hardcoded value of 17 in their code. When I ran the game on debug mode with the FPS shown, I saw it, FPS was exactly 17! I look over the code again and now it's clear: the programmers assumed that the game will always have a 17 FPS constant frame rate. If the FPS was greater than 17, they did a sleep to make the FPS be exactly 17. Of course, they did nothing if the FPS was smaller than 17 the game just went crazy (like when played at 2 FPS and driving a car in the game, the game system alerted me: "Too Fast! Too Fast!").
So I write an email asking why they hardcoded this value and use it their physics engine and they replied that this way they keep the engine simpler. And i replied again, Ok, but if we run the game on a device that is incapable of 17 FPS, your game engine runs very funny but not as expected. And they said that will fix the issue until the next code review.
After 3 or 4 weeks I get a new version of the source code so I was really curious to find out what they did with the FPS constant so first thing i do is search through code after 17 and there are only a couple matches, but one of them was not something i wanted to see:
final static int FPS = 17;
So they removed all the hardcoded 17 value from all the code and used the FPS constant instead. And their motivation: now if I need to put the game on a device that can only do 10 FPS, all i need to do is to set that FPS constant to 10 and the game will work smooth.
In conclusion, sorry for writing such a long message, but I wanted to emphasize that the only reason why anyone will do such a thing is the bad design.
Here's a good explanation on why your timestep should be kept constant: http://gafferongames.com/game-physics/fix-your-timestep/
Additionally, depending on the physics engine, the system may get unstable when the timestep changes. This is because some of the data that is cached between frames is timestep-dependant. For example, the starting guess for an iterative solver (which is how constraints are solved) may be far off from the answer. I know this is true for Havok (the physics engine used by many commericial games), but I'm not sure which engine SMB uses.
There was also an article in Game Developer Magazine a few months ago, illustrating how a jump with the same initial velocity but different timesteps was achieved different max heights with different frame rates. There was a supporting anecdote from a game (Tony Hawk?) where a certain jump could be made when running on the NTSC version of the game but not the PAL version (since the framerates are different). Sorry I can't find the issue at the moment, but I can try to dig it up later if you want.
They probably needed to get the game done quickly enough and decided that they would cover sufficient user base with the current implementation.
Now, it's not really that hard to retrofit independence, if you think about it during development, but I suppose they could go down some steep holes.
I think it's unnecessary, and I've seen it before (some early 3d-hw game used the same thing, where the game went faster if you looked at the sky, and slower if you looked at the ground).
It just sucks. Bug the developers about it and hope that they patch it, if they can.
Is there any documentation on how to write software that uses the framebuffer device in Linux? I've seen a couple simple examples that basically say: "open it, mmap it, write pixels to mapped area." But no comprehensive documentation on how to use the different IOCTLS for it anything. I've seen references to "panning" and other capabilities but "googling it" gives way too many hits of useless information.
Edit:
Is the only documentation from a programming standpoint, not a "User's howto configure your system to use the fb," documentation the code?
You could have a look at fbi's source code, an image viewer which uses the linux framebuffer. You can get it here : http://linux.bytesex.org/fbida/
-- It appears there might not be too many options possible to programming with the fb from user space on a desktop beyond what you mentioned. This might be one reason why some of the docs are so old. Look at this howto for device driver writers and which is referenced from some official linux docs: www.linux-fbdev.org [slash] HOWTO [slash] index.html . It does not reference too many interfaces.. although looking at the linux source tree does offer larger code examples.
-- opentom.org [slash] Hardware_Framebuffer is not for a desktop environment. It reinforces the main methodology, but it does seem to avoid explaining all the ingredients necessary to doing the "fast" double buffer switching it mentions. Another one for a different device and which leaves some key buffering details out is wiki.gp2x.org [slash] wiki [slash] Writing_to_the_framebuffer_device , although it does at least suggest you might be able use fb1 and fb0 to engage double buffering (on this device.. though for desktop, fb1 may not be possible or it may access different hardware), that using volatile keyword might be appropriate, and that we should pay attention to the vsync.
-- asm.sourceforge.net [slash] articles [slash] fb.html assembly language routines that also appear (?) to just do the basics of querying, opening, setting a few basics, mmap, drawing pixel values to storage, and copying over to the fb memory (making sure to use a short stosb loop, I suppose, rather than some longer approach).
-- Beware of 16 bpp comments when googling Linux frame buffer: I used fbgrab and fb2png during an X session to no avail. These each rendered an image that suggested a snapshot of my desktop screen as if the picture of the desktop had been taken using a very bad camera, underwater, and then overexposed in a dark room. The image was completely broken in color, size, and missing much detail (dotted all over with pixel colors that didn't belong). It seems that /proc /sys on the computer I used (new kernel with at most minor modifications.. from a PCLOS derivative) claim that fb0 uses 16 bpp, and most things I googled stated something along those lines, but experiments lead me to a very different conclusion. Besides the results of these two failures from standard frame buffer grab utilities (for the versions held by this distro) that may have assumed 16 bits, I had a different successful test result treating frame buffer pixel data as 32 bits. I created a file from data pulled in via cat /dev/fb0. The file's size ended up being 1920000. I then wrote a small C program to try and manipulate that data (under the assumption it was pixel data in some encoding or other). I nailed it eventually, and the pixel format matched exactly what I had gotten from X when queried (TrueColor RGB 8 bits, no alpha but padded to 32 bits). Notice another clue: my screen resolution of 800x600 times 4 bytes gives 1920000 exactly. The 16 bit approaches I tried initially all produced a similar broken image to fbgrap, so it's not like if I may not have been looking at the right data. [Let me know if you want the code I used to test the data. Basically I just read in the entire fb0 dump and then spit it back out to file, after adding a header "P6\n800 600\n255\n" that creates the suitable ppm file, and while looping over all the pixels manipulating their order or expanding them,.. with the end successful result for me being to drop every 4th byte and switch the first and third in every 4 byte unit. In short, I turned the apparent BGRA fb0 dump into a ppm RGB file. ppm can be viewed with many pic viewers on Linux.]
-- You may want to reconsider the reasons for wanting to program using fb0 (this might also account for why few examples exist). You may not achieve any worthwhile performance gains over X (this was my, if limited, experience) while giving up benefits of using X. This reason might also account for why few code examples exist.
-- Note that DirectFB is not fb. DirectFB has of late gotten more love than the older fb, as it is more focused on the sexier 3d hw accel. If you want to render to a desktop screen as fast as possible without leveraging 3d hardware accel (or even 2d hw accel), then fb might be fine but won't give you anything much that X doesn't give you. X apparently uses fb, and the overhead is likely negligible compared to other costs your program will likely have (don't call X in any tight loop, but instead at the end once you have set up all the pixels for the frame). On the other hand, it can be neat to play around with fb as covered in this comment: Paint Pixels to Screen via Linux FrameBuffer
Check for MPlayer sources.
Under the /libvo directory there are a lot of Video Output plugins used by Mplayer to display multimedia. There you can find the fbdev (vo_fbdev* sources) plugin which uses the Linux frame buffer.
There are a lot of ioctl calls, with the following codes:
FBIOGET_VSCREENINFO
FBIOPUT_VSCREENINFO
FBIOGET_FSCREENINFO
FBIOGETCMAP
FBIOPUTCMAP
FBIOPAN_DISPLAY
It's not like a good documentation, but this is surely a good application implementation.
Look at source code of any of: fbxat,fbida, fbterm, fbtv, directFB library, libxineliboutput-fbe, ppmtofb, xserver-fbdev all are debian packages apps. Just apt-get source from debian libraries. there are many others...
hint: search for framebuffer in package description using your favorite package manager.
ok, even if reading the code is sometimes called "Guru documentation" it can be a bit too much to actually do it.
The source to any splash screen (i.e. during booting) should give you a good start.