Fast set/getPixel for an opengl texture?

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Fast set/getPixel for an opengl texture?

(77 posts) (21 voices)

Started 2 years ago by Lam
Latest reply from JanuszNSG

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mungler
Member
Hmm.. ok, making some progress, but not quite what i'd hoped.

I've got a background/scenery image (currently a Sprite, but soon to be a tilemap).

When I create this sprite, I use:
```
UIImage *scenery = [UIImage imageNamed:@"scenerylayer.png"];
_sceneryTexture = [[CCMutableTexture2D alloc] initWithImage:scenery];
_scenerylayer = [CCSprite spriteWithTexture:_sceneryTexture];
```
Which is all fine and dandy.

Later, when I want to draw a pixel onto the background, I do this:
```
ccColor4B black = ccc4(0,0,0,1);
[_sceneryTexture setPixelAt:[_ship getSprite].position rgba: black];
_scenerylayer.dirty = YES;
```
I was hoping this would draw a black pixel at the position of my _ship actor, but the scenery doesn't change.

I also tried [_sceneryTexture fill:black] in case it was some kind of coordinate mismatch, but still nothing changes.

Can anyone see anything obviously wrong here? Any help most appreciated!
Posted 1 year ago #
Lam
Member

ok that's good that you got it working. :)

Since setting a pixel is an expensive call. I had to make an 'apply' method in the CCMutableTexture.

So after you set a few pixels, call apply to actually apply it to the texture.

Posted 1 year ago #
mungler
Member

ahh great! thought it might be something simple :D

thankyou, i'll try it now :)

EDIT: yay it works! though since im using the sprite position the y is inverted, but i'll soon have that fixed :)

ultimately, i want to 'delete' (mark black) pixels in the shape of my ship, in its current rotation. i'm guessing that since rotation is done in hardware, even if i make my ship use a MutableTexture, i wont be able to access the pixels in their rotated state, right?

can you think of an easy way to achieve this?

Posted 1 year ago #
Lam
Member

@mungler
Yeah I'm sure adding rotation complicates the logic. I'm not even sure an exact solution to that yet.

Probably what you would do is some coordinate conversion (converToWorldSpace, convertToNodeSpace) to then relate it to the index coordinate in the texture matrix.

Posted 1 year ago #
mungler
Member

I was thinking maybe I could rotate the texture and render it to some offscreen buffer and then bitwise AND with the background texture to figure out which pixels are to be deleted, then setPixelAt each of them to black.

however, i haven't the slightest idea how to do that :) i'm a total OpenGL n00b unf.

Thanks again for your help :)

Posted 1 year ago #
mungler
Member

Hey Lam, or anyone else who wants to help ;)

One question - is it possible to have a fast (ie OpenGL-based, or at least hardware accelerated) 'draw triangle' routine built into this MutableTexture class?

ie I want to draw a triangle onto the texture. right now im using my own scan conversion algorithm and then plotting the triangle with multiple SetPixelAt calls, but it kills performance - drops to around 6fps in simulator. :(

Posted 1 year ago #
bradparks
Member

hey @mungler.... i don't know if this'll help or not, but here's a post for a routine that draws a filled polygon using OpenGL:

http://www.cocos2d-iphone.org/forum/topic/7511#post-44014

and here's a post for checking if a rotated sprite intersects a point (ie pixel coordinate, I'm thinking)... the idea behind the solutions posted for this is that instead of testing if your rotated sprite intersects a pt, you test for a rotated pt in the -angle intersecting your non rotated sprite.... so maybe the same would work for you!

http://www.cocos2d-iphone.org/forum/topic/7150#post-42140

hope it helps!

Posted 1 year ago #
mungler
Member

hey @bradparks - wow, those both look totally ideal for what I want to do!

Thank you for pointing them out :D

Posted 1 year ago #
mungler
Member

am i right in thinking i have to call the OpenGL drawing stuff in the draw method?

so, in the game logic, should i be building a queue of shapes I want drawn on the next pass?

do i have to worry about thread safety? :)

Posted 1 year ago #
Lam
Member

Yeah you draw any needed shapes in the draw call and an easy way to draw multiple shapes is through a list or queue kind of similar to how cocos2d handles the rendering of children.

And you don't have to worry about thread issues in cocos2d. Well unless you start implementing your own multithreaded system.

Posted 1 year ago #
mungler
Member

Thx again Lam :)

Posted 1 year ago #
jptsetung
Member
@Lam I'm playing with your class righ now. It's an impressive piece of code and I'm learning a lot with it. Thx.
I'm trying to imrove and add a few methods to the class, like fillPolygon, and I will share the result if I can make it work.

I have a question for my understanding. I don't understand why you set a pixel with pixel[(y * width_) + x] =... in the case of an uint and with pixel = pixel + (y * width_) + x; *pixel =... in the case of a GLushort. Why not using pixel[(y * width_) + x] =... in both cases ?
```
if(format_ == kTexture2DPixelFormat_RGBA8888){
        uint *pixel = data_;
        pixel[(y * width_) + x] = (c.a << 24) | (c.b << 16) | (c.g << 8) | c.r;
} else if(format_ == kTexture2DPixelFormat_RGBA4444){
        GLushort *pixel = data_;
        pixel = pixel + (y * width_) + x;
        *pixel = ((c.r >> 4) << 12) | ((c.g >> 4) << 8) | ((c.b >> 4) << 4) | (c.a >> 4);
}
```
Posted 1 year ago #
jptsetung
Member

Additional question, I get a BAD ACCESS exception when using applyWithAsyncObject:

at this line
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, width_, height_, 0, GL_RGBA, GL_UNSIGNED_BYTE, data_);

What is the correct use of this method ?

Posted 1 year ago #
Lam
Member

I have a question for my understanding. I don't understand why you set a pixel with pixel[(y * width_) + x] =... in the case of an uint and with pixel = pixel + (y * width_) + x; *pixel =... in the case of a GLushort. Why not using pixel[(y * width_) + x] =... in both cases ?

Hehe. Uh... it's probably because I'm wacky :)
Yeah both lines really mean the same thing in the end. But it's awesome to see alternate ways of accessing an array! Honest!

Additional question, I get a BAD ACCESS exception when using applyWithAsyncObject:

oh yeah i think i'll have to trace the error with applyWithAsyncObject but yeah it's not on your end. I seem to be having problems with that too.

Posted 1 year ago #
jptsetung
Member

Oh I hadn't see you had replied, thx a lot.

I endded with not using the multithread apply as it's too instable and I can't find a way to correct it. I splitted my drawings in smaller pieces which is a kind of custom multithreaded drawing.

Posted 1 year ago #
Dima
Member
I got it working easy. Thanks. But I noticed that when I just change pixels opacity to 0 (transparent) and create sprite from changed texture it is not fully transparent as I expected. Definitely picture has some transparent level, but not 0. Format RGBA8888. What is the reason? Premultiplied alpha value?
```
for (i = 0; i < height; i++)
{
	for (j = 0; j < width; j++)
	{
		dstPoint.x=j;
		dstPoint.y=i;

		pxDst = [colorMutTex pixelAt:dstPoint];
		pxDst.a = 0;

	        [colorMutTex setPixelAt:dstPoint rgba:pxDst];
	}
}

	[colorMutTex apply];

	CCSprite *colorSprite = [CCSprite spriteWithTexture:colorMutTex];
```
Posted 1 year ago #
Dima
Member

The reason of such behavior is blending mode. Blendind setting fixes issue:

CCSprite *colorSprite = [CCSprite spriteWithTexture:(CCTexture2D*)colorMutTex];
[colorSprite setBlendFunc:(ccBlendFunc) {GL_SRC_ALPHA,GL_ONE_MINUS_SRC_ALPHA}];

Posted 1 year ago #
plumenator
Member

Shouldn't setPixelAt:rgba: premultiply the rgb with a? Or does the method expect premultipled colors? Similarly shouldn't pixelAt: undo the premultiplication (which is unfortunately lossy, of course)?.

Posted 1 year ago #
plumenator
Member

@Lam Btw, Have you gotten around to optimizing the code with glTexSubImage? I tried a similar thing by maintaining a dirty rect and applying it on draw. Never worked. :-(

Posted 1 year ago #
iphonerider
Member

Any new solution about this?

Posted 10 months ago #
Lam
Member

oh haha whoops sorry guys. Didn't notice the questions.

I wonder if mutable texture should take care of premultiplied alpha or should the decision to change blend func be on the programmers end.

If Apple's improved the glTexSubImage that might be an improvement over a direct call to all pixels. I have to take a look at it when I have the time (sorry not much time these days on my end) but I'd have to do some extensive testing just to make sure that the alternative is actually efficient.

Posted 10 months ago #
seecah.khing
Member

@Lam: Any progress on this? This stuff is very useful but I can't let it work. Would you mine sharing a sample code using your API. My apology since I'm still new to Cocos2d.

Thanks a lot!

Posted 4 months ago #
Lam
Member

@seecah.khing
Just do a forum search for "CCMutableTexture". There's quite a lot of posts of people with example code for it.

Here's one example of gaussian blur from manucorporat. Maybe that'll be easy to see how the class is used.
http://www.cocos2d-iphone.org/forum/topic/6315

Posted 4 months ago #
seecah.khing
Member

@Lam: Thank you so much for the guidance.. I'll check this out.

Posted 4 months ago #
Birkemose
Member

I do extensive manipulation on full screen images ( iPhone ), and by far the fastest approach I have come up with, is copying the entire screen buffer ( in my case live video ) to a memory buffer, doing the manipulations on this buffer, and then render it, using glTexSubImage2D.

Copying the entire screenbuffer, is much less costly than you would think. It uses DMA and does not halt the render pipeline. Just a few glReadPixels will be just as time consuming. I have read people saying, that glTexSubImage2D is slow. I dont think that is the case, it should be just as fast as any other image rendered by OpenGL. Probably what confuses people, is, that when they use subimages, it is easy ( just like with glReadPixels ) to mess up the render pipeline, and kill performance.

My 2 cents anyways.

EDIT:
Maybe I should add, that depending on needs, it might be an option to copy the entire content to an offscrren OpenGL surface. That would be quicker if you had a lot of stuff to render. I do a lot of reading data, but no offscreen rendering, so in my case I have no use of an off screen OpenGL surface.

Posted 4 months ago #
seecah.khing
Member

@Lam: I wonder if I can use this one for coloring a sprite. I need to like painting a sprite through the fingers just like Color Me. I'm still so very new in cocos2d and hopefully you can guide me through. Thanks

Posted 4 months ago #
Lam
Member

@seecah.khing
Yeah this should be doable with mutable texture. Just make sure to search the forum and try out the examples to see if you figure out the basics of using the class first.

Posted 4 months ago #
seecah.khing
Member
@Lam: I have already tried everything on importing you class and I forgot to tell you that I'm using the alpha release of cocos2d with versioin 2.0 but I got a lot of errors one of those is the undeclared identifier for the variables below:
```
case kTexture2DPixelFormat_RGBA8888:	bytesPerPixel_ = 4; break;
			case kTexture2DPixelFormat_A8:			bytesPerPixel_ = 1; break;
			case kTexture2DPixelFormat_RGBA4444:
			case kTexture2DPixelFormat_RGB565:
			case kTexture2DPixelFormat_RGB5A1:
```
Please advice.

Edited: Never mind I got it already, I've just realized that they changed these variables to eg. kTexture2DPixelFormat_A8 => kCCTexture2DPixelFormat_A8.
Posted 4 months ago #
zaaroth
Member

@Lam will know for sure, but, as far as I know, the mutable texture is a rather untested class. Even though lots of people make use of it one way or another, it is not guaranteed to work through automated tests of the framework, so it might break during an upgrade.

Since 2.0 is really in its early stages it is not unexpected that it does not work.

Posted 4 months ago #
JanuszNSG
Member

Hello to all:)
I have strange problem with compiling CCMutableTexture, even in empty cocos2d project, is I add both files recieve 41 errors.
Eg.
- Not known Texture2DPixelFormat
- a lot of undeclared variables (_size, _width ...)

I'm using cocos 0.99.5 and XCode 3.2.6 - meybe there is a problem?

Posted 4 months ago #

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