Alpha blending to draw buffer?

ne0h · Post by **ne0h** » Fri Dec 18, 2009 6:48 am

It's that possible?
That's the function that I'm using:

void XgeFillScreenRect&#40;XgeColor Color, int x0, int y0, int width, int height&#41;
&#123;
    int skipX = PSP_LINE_SIZE - width;
    int x, y;
    XgeColor* data = XgeGetVramDrawBuffer&#40;&#41; + x0 + y0 * PSP_LINE_SIZE;
    for&#40;y = 0; y < height; y++, data += skipX&#41;
    &#123;
        for&#40;x = 0; x < width; x++, data++&#41;
            *data = Color;
    &#125;
&#125;

There's a way to do the same thing but with alpha?
Thanks,

ne0h

a_noob · Post by **a_noob** » Fri Dec 18, 2009 10:36 am

Its possible but it would be much better to use the GU.

alpha blending would be something like.

Code: Select all

inline unsigned int RGBA&#40;unsigned int R, unsigned int G, unsigned int B, unsigned int A&#41;
&#123;
	return &#40;unsigned int&#41;&#40;&#40;A & 0xFF&#41; << 24 | 
						  &#40;R & 0XFF&#41; << 16 | 
						  &#40;G & 0XFF&#41; << 8 |
						  &#40;B & 0XFF&#41;&#41;;
&#125;

unsigned int alphaBlend&#40;unsigned int a, unsigned int b&#41;&#123;
	float aa = 255.f/&#40;a>>24&0xff&#41;;// A colors alpha channel as a float 0 - 1
	float ba = 255.f/&#40;b>>24&0xff&#41;;// B colors alpha channel as a float 0 - 1
	
	char ar = aa * &#40;a&0xff&#41;;//alpha influenced
	char ag = aa * &#40;a>>8&0xff&#41;;
	char ab = aa * &#40;a>>16&0xff&#41;;
	
	char br = ba * &#40;b&0xff&#41;;//alpha influenced
	char bg = ba * &#40;b>>8&0xff&#41;;
	char bb = ba * &#40;b>>16&0xff&#41;;
	
	return RGBA&#40;ar+br,ag+bg,ab+bb,&#40;a+b&#41;*255&#41;;
	
&#125;

ne0h · Post by **ne0h** » Sat Dec 19, 2009 1:59 am

Excuse me, I didn't explain my problem as I wanted...
When I use the function with alpha like this:

Code: Select all

XgeFillScreenRect&#40;0x50FF0000, X, Y, Width, Height&#41;;

i won't get an rectange with trasparency....

carl0sgs · Post by **carl0sgs** » Sat Dec 19, 2009 3:30 am

I think the function that a_noob wrote is for blending two colors.
Like this:

Code: Select all

mixedColor = alphaBlend&#40;RGB&#40;100,200,50&#41;, RGB&#40;200,100,150&#41;&#41;;

Should return the resulting color.

So you would have this function (i think):

Code: Select all

unsigned int RGBA&#40;unsigned int R, unsigned int G, unsigned int B, unsigned int A&#41;
&#123;
   return &#40;unsigned int&#41;&#40;&#40;A & 0xFF&#41; << 24 |
                    &#40;R & 0XFF&#41; << 16 |
                    &#40;G & 0XFF&#41; << 8 |
                    &#40;B & 0XFF&#41;&#41;;
&#125;

unsigned int alphaBlend&#40;unsigned int a, unsigned int b&#41;&#123;
   float aa = 255.f/&#40;a>>24&0xff&#41;;// A colors alpha channel as a float 0 - 1
   float ba = 255.f/&#40;b>>24&0xff&#41;;// B colors alpha channel as a float 0 - 1
   
   char ar = aa * &#40;a&0xff&#41;;//alpha influenced
   char ag = aa * &#40;a>>8&0xff&#41;;
   char ab = aa * &#40;a>>16&0xff&#41;;
   
   char br = ba * &#40;b&0xff&#41;;//alpha influenced
   char bg = ba * &#40;b>>8&0xff&#41;;
   char bb = ba * &#40;b>>16&0xff&#41;;
   
   return RGBA&#40;ar+br,ag+bg,ab+bb,&#40;a+b&#41;*255&#41;;
   
&#125; 

void XgeFillScreenRect&#40;XgeColor Color, int x0, int y0, int width, int height&#41;
&#123;
    int skipX = PSP_LINE_SIZE - width;
    int x, y;
    XgeColor* data = XgeGetVramDrawBuffer&#40;&#41; + x0 + y0 * PSP_LINE_SIZE;
    for&#40;y = 0; y < height; y++, data += skipX&#41;
    &#123;
        for&#40;x = 0; x < width; x++, data++&#41;
            *data = alphaBlend&#40;Color,data&#41;;//We put the mixed color
    &#125;
&#125;

I hope that works!

ne0h · Post by **ne0h** » Sat Dec 19, 2009 3:53 am

O_O
omg...
Anyway, I'll try...

carl0sgs · Post by **carl0sgs** » Sat Dec 19, 2009 4:06 am

OK, it works!
Thanks to both of you, you helped me a lot :-P
Now I can blend alpha images in multitasking :-)

@ne0h Good luck with Xplora, it is a really useful program :-D

Thanks again,
Carlos

ne0h · Post by **ne0h** » Sat Dec 19, 2009 4:37 am

Nevermind, resolved...
But now I get something like:

There's a way to do something like this funct but with only one color?

Code: Select all

sceGuTexImage

Like a monocrome texture?

carl0sgs · Post by **carl0sgs** » Sat Dec 19, 2009 5:13 am

OK
You have to mix two colors because you want to put one color over the other one.

I don't know why that is not working, I let you this piece of code:

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#define RGBA&#40;r, g, b, a&#41; &#40;&#40;r&#41;|&#40;&#40;g&#41;<<8&#41;|&#40;&#40;b&#41;<<16&#41;|&#40;&#40;a&#41;<<24&#41;&#41; //Use this instead of the other function

void blitAlphaImageToImage&#40;int sx, int sy, int width, int height, Image* source, int dx, int dy, Image* destination&#41;//With alpha
&#123;
	// TODO Blend! - Done! xD
	Color* destinationData = &destination->data&#91;destination->textureWidth * dy + dx&#93;;
	int destinationSkipX = destination->textureWidth - width;
	Color* sourceData = &source->data&#91;source->textureWidth * sy + sx&#93;;
	int sourceSkipX = source->textureWidth - width;
	int x, y;
	for &#40;y = 0; y < height; y++, destinationData += destinationSkipX, sourceData += sourceSkipX&#41; &#123;
		for &#40;x = 0; x < width; x++, destinationData++, sourceData++&#41; &#123;
			Color color = *sourceData;
			*destinationData = alphaBlend&#40;*destinationData,color&#41;;
		&#125;
	&#125;
&#125;

This is what works for me, I haven't tested the rectangle function, sorry :-S

carl0sgs · Post by **carl0sgs** » Sat Dec 19, 2009 5:16 am

ne0h wrote:Nevermind, resolved...
But now I get something like:

There's a way to do something like this funct but with only one color?
Code: Select all
sceGuTexImage
Like a monocrome texture?

No idea of how did you got that :-S
It is not possible to do that alpha blending without using two colors, maybe with the GU, but that would do the same thing really.

Sorry :-S

ne0h · Post by **ne0h** » Sat Dec 19, 2009 5:20 am

I don't use images but fillscreenrect only for memory purposes...
I want to find a way to draw an alpha rectangle on the screen,
just like sceGuTexImage, but without loading something like 1MB of image...
Anyway sorry for misunderstanding with the two colors and thanks both.

ne0h

carl0sgs · Post by **carl0sgs** » Sat Dec 19, 2009 5:31 am

I think you should change the alpha values

a_noob · Post by **a_noob** » Sat Dec 19, 2009 6:55 am

oh its my bad for the b alpha you need to do 1 - the alpha. So

Code: Select all

unsigned int alphaBlend&#40;unsigned int a, unsigned int b&#41;&#123; 
   float aa = 255.f/&#40;a>>24&0xff&#41;;// A colors alpha channel as a float 0 - 1 
   float ba = 1.f-&#40;255.f/&#40;b>>24&0xff&#41;&#41;;// B colors alpha channel as a float 0 - 1 
    
   unsigned char ar = aa * &#40;a&0xff&#41;;//alpha influenced 
   unsigned char ag = aa * &#40;a>>8&0xff&#41;; 
   unsigned char ab = aa * &#40;a>>16&0xff&#41;; 
    
   unsigned char br = ba * &#40;b&0xff&#41;;//alpha influenced 
   unsigned char bg = ba * &#40;b>>8&0xff&#41;; 
   unsigned char bb = ba * &#40;b>>16&0xff&#41;; 
    
   return RGBA&#40;ar+br,ag+bg,ab+bb,&#40;a+b&#41;*255&#41;; 
    
&#125;

should do the trick.

I do advise switching to the GU as this is terribly slow on the CPU, you need to do this calculation for each pixel :/ where as the GPU has built in hardware blending procedures which are extremely fast.

-=EDIT=-

Oh crap and the psp uses 0xAABBGGRR not 0xAARRGGBB so this is the updated RGBA func

Code: Select all

unsigned int RGBA&#40;unsigned int R, unsigned int G, unsigned int B, unsigned int A&#41; 
&#123; 
   return &#40;unsigned int&#41;&#40;&#40;A & 0xFF&#41; << 24 | &#40;B & 0XFF&#41; << 16 | &#40;G & 0XFF&#41; << 8 | &#40;R & 0XFF&#41;&#41;; 
&#125;

carl0sgs · Post by **carl0sgs** » Sat Dec 19, 2009 7:44 am

Good!
Thanks for the updated function ;-)

Raphael · Post by **Raphael** » Sat Dec 19, 2009 8:06 am

Just for note: It should be 1-aalpha, if anything, for the common alpha blending behaviour.
Still, this software solution is stupid for anything else but learning how alpha blending works.

ne0h · Post by **ne0h** » Sun Dec 20, 2009 3:48 am

I would like to use sceGu, but how?
I've never used very much sceGu...

Raphael · Post by **Raphael** » Sun Dec 20, 2009 5:30 am

pspsdk/samples/gu is your first source of information. Afterwards, there are lots of open source graphical engines available, that you can learn from, like OSlib or triEngine to name only two.
Using gu is very simple. It's just a matter of a little time investment to learn the concepts of a state machine and a very basic graphics api. If you have some pre-knowledge on OpenGL it's easy as cake.

Torch · Post by **Torch** » Sun Dec 20, 2009 1:38 pm

For software, you need to check the display mode and calculate accordingly.

Use the getdisplaymode or whatever first to read the pixelformat. See the DrawImage() function.

http://code.google.com/p/lockdownpack/s ... ame/main.c