SDL_GetVideoInfo and ofstream

Engines and Middleware Programming

Started by Onlydying April 01, 2010 10:58 AM

9 comments, last by rip-off 14 years ago

104

Author

April 01, 2010 10:58 AM

I've been reading through "Focus on SDL" and one of the functions I'm learning about is SDL_GetVideoInfo(), yet im programming in c++ and have been using ofstream instead of fprintf (I think I'm right in saying that is C). Problem is when I use ofstream to print the results to a txt I'm getting the wrong results. This is the code:


g_pVideoInfo = SDL_GetVideoInfo();
	std:: ofstream VIDEOlog;
	VIDEOlog.open("VIDEO Logfile.txt");
	VIDEOlog << "-Video Information:\n\n" <<
		"-hw_available:\t\t" << g_pVideoInfo->hw_available << "\n" <<
		"-wm_available:\t\t" << g_pVideoInfo->wm_available << "\n" <<
		"-blit_hw: \t\t" << g_pVideoInfo->blit_hw << "\n" <<
		"-blit_hw_CC: \t\t" << g_pVideoInfo->blit_hw_CC << "\n" <<
		"-blit_hw_A: \t\t" << g_pVideoInfo->blit_hw_A << "\n" <<
		"-blit_sw: \t\t" << g_pVideoInfo->blit_sw << "\n" <<
		"-blit_sw_CC: \t\t" << g_pVideoInfo->blit_sw_CC << "\n" <<
		"-blit_sw_A: \t\t" << g_pVideoInfo->blit_sw_A << "\n" <<
		"-blit_fill: \t\t" << g_pVideoInfo->blit_fill << "\n" <<
		"-video memory(in K): \t" << g_pVideoInfo->video_mem << "\n" <<
		"-bits per pixel: \t" << g_pVideoInfo->vfmt->BitsPerPixel << "\n";
	VIDEOlog.close();

And the results for this are:

Quote: -Video Information: -hw_available: 0 -wm_available: 1 -blit_hw: 0 -blit_hw_CC: 0 -blit_hw_A: 0 -blit_sw: 0 -blit_sw_CC: 0 -blit_sw_A: 0 -blit_fill: 0 -video memory(in K): 0 -bits per pixel:

Any help would be greatly appreciated. Am I wrong to use ofstream in this situation?

Kylotan

10,510

April 01, 2010 11:07 AM

How do you know the results are wrong?

fprintf is part of C++ too. You can use C functions in C++ if you like. Try both and compare the output.

Onlydying

104

Author

April 01, 2010 11:13 AM

Quote:Original post by Kylotan
How do you know the results are wrong?

fprintf is part of C++ too. You can use C functions in C++ if you like. Try both and compare the output.

I'm sure I have than 0kb maximum video memory lol and it doesnt even print out the colour format, in the example in the book the guys results were mostly = 1 whereas all mine are 0 except 1, and I'm fairly sure that cant be right, I could be wrong of course. That's what has brought me to believe they're probably not right bt i still need a lot to learn :)

And I know you can use C functions etc but there's alot to take in and I feel more comfortable with ofstream atm, although I'll try using fstreamf as you suggest to see what I get.

Gage64

1,235

April 01, 2010 11:16 AM

I think the problem is because SDL_VideoInfo uses bitfields for a lot of its members (see here).

I'm not too familiar with those, but try this:

VIDEOlog << "-Video Information:\n\n" <<	    "-hw_available:\t\t" << (g_pVideoInfo->hw_available == 1) << "\n" <<	    "-wm_available:\t\t" << (g_pVideoInfo->wm_available == 1) << "\n" <<            // etc.

Only add the comparisons to the fields that have :1 to the right (see link above). For example, video_mem should be printed as usual.

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Zakwayda

2,389

April 01, 2010 11:17 AM

Generally speaking, there should be no problem writing the information to a C++ stream object.

Quote:And the results for this are:

Quote:
-Video Information:

-hw_available: 0
-wm_available: 1
-blit_hw: 0
-blit_hw_CC: 0
-blit_hw_A: 0
-blit_sw: 0
-blit_sw_CC: 0
-blit_sw_A: 0
-blit_fill: 0
-video memory(in K): 0
-bits per pixel:

What's the expected output? Also, what do you get if you use C library functions (e.g. printf()) instead?

[Edit: Too slow x3.]

Onlydying

104

Author

April 01, 2010 11:40 AM

Quote:Original post by Gage64
I think the problem is because SDL_VideoInfo uses bitfields for a lot of its members (see here).

I'm not too familiar with those, but try this:
VIDEOlog << "-Video Information:\n\n" <<	    "-hw_available:\t\t" << (g_pVideoInfo->hw_available == 1) << "\n" <<	    "-wm_available:\t\t" << (g_pVideoInfo->wm_available == 1) << "\n" <<            // etc.
Only add the comparisons to the fields that have :1 to the right (see link above). For example, video_mem should be printed as usual.

It shows the exact same results. I ran it on my laptop also, dif OS etc shows exactly the same results. And I also use fprintf and still the same results lol

@JYK:
I believe this little test pretty much tells me what my system is capable of when it comes down to SDL, for example hw_available == 1 would be telling me I can draw in hardware mode as oppose to software mode which my 8800gt is capable of, hope I'm getting this right, I hate not being so sure haha So yeah i expect my system to be capable of most if not all of these things so they should be at 1 I believe.
Considering all this and it giving the same results on my laptop I must have some fault with my code somewhere or other hmm

Thanks for the feedback btw guys :)

Gage64

1,235

April 01, 2010 11:53 AM

I just ran a similar test on my system, and got the same results.

A couple of things to note from the link I gave earlier:

Quote:video_mem
Total amount of video memory in Kilobytes, should be accessed only if hw_available == 1, otherwise it is equal to 0

That explains the video memory.

Also:

Quote:SDL_GetVideoInfo ... contains information on either the best available mode if called before SDL_SetVideoMode or the current video mode if called after SDL_SetVideoMode.

though on my system only current_w/y were different, the other fields were still 0 (except for wm_available, which was 1).

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Onlydying

104

Author

April 01, 2010 12:06 PM

Quote:Original post by Gage64
I just ran a similar test on my system, and got the same results.

A couple of things to note from the link I gave earlier:

Quote:video_mem
Total amount of video memory in Kilobytes, should be accessed only if hw_available == 1, otherwise it is equal to 0

That explains the video memory.

Also:

Quote:SDL_GetVideoInfo ... contains information on either the best available mode if called before SDL_SetVideoMode or the current video mode if called after SDL_SetVideoMode.

though on my system only current_w/y were different, the other fields were still 0 (except for wm_available, which was 1).

Lol so maybe I'm getting the correct results then, It's the guys results in the book that are confusing me now, his were:

Quote:
Video Information:
hw_available? 1
wm_available? 1
blit_hw? 1
blit_hw_CC? 1
blit_hw_A? 0
blit_sw? 1
blit_sw_CC? 1
blit_sw_A? 0
blit_fill? 1
video memory(in K)? 36864
bits per pixel? 16

I'm in the very early stages of learning SDL btw, things may become clearer once I learn a few more things lol

I get the same results whether SDL_GetVideoInfo is called either before or after too btw

rip-off

11,000

April 01, 2010 12:29 PM

You might be able to get hardware acceleration by changing the video backend. For instance, on Windows about a year ago the default backend was moved from Direct2D to GDI. You can force SDL to choose a particular backend like so. Do be aware that each backend has trade-offs - critically hardware acceleration does not imply speed increases.

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Onlydying

104

Author

April 01, 2010 12:58 PM

Quote:Original post by rip-off
You might be able to get hardware acceleration by changing the video backend. For instance, on Windows about a year ago the default backend was moved from Direct2D to GDI. You can force SDL to choose a particular backend like so. Do be aware that each backend has trade-offs - critically hardware acceleration does not imply speed increases.

hey nice, thanks, I'm getting similar results I initially expected now:

Quote:
-Video Information:

-hw_available: 1
-wm_available: 1
-blit_hw: 1
-blit_hw_CC: 1
-blit_hw_A: 0
-blit_sw: 1
-blit_sw_CC: 1
-blit_sw_A: 0
-blit_fill: 1
-video memory(in K): 253960
-bits per pixel:

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