bitblt function

[webjeff]

Hello coders,

does bitblt function account for alpha? How does that work, my image is now loading correct but I can't get the alpha to work. it should be in the right format cause RGB is coming up correctly, so what needs to be done to get alpha working?

Thanks
Jeff.

[Orion_]

modify the function to support alpha :)

[blackdroid]

since you are uploading it to vram directly and not doing it via gpu pipeline you have to do the alpha calculation yourself.

[Tychom]

well fwiw I knocked together a very quick and dirty alpha blending function last night for my game which is just an extension of the current - note this is bound to be terribly slow but it does at least work ;)

Code: Select all

#define MASK_RED	0x1F
#define MASK_GREEN	0x3E0
#define MASK_BLUE	0x7C00

#define GET_RED&#40;c&#41; &#40;&#40;unsigned char&#41;&#40;&#40;c & MASK_RED&#41; << 3&#41;&#41;
#define GET_GREEN&#40;c&#41; &#40;&#40;unsigned char&#41;&#40;&#40;c & MASK_GREEN&#41; >> 2&#41;&#41;
#define GET_BLUE&#40;c&#41; &#40;&#40;unsigned char&#41;&#40;&#40;c & MASK_BLUE&#41; >> 7&#41;&#41;

unsigned short alpha_blend&#40;unsigned short front, unsigned short back, unsigned char alpha&#41;
&#123;
	unsigned char beta = 255 - alpha;

	return rgb2col&#40;
		&#40;&#40;GET_RED&#40;front&#41; * alpha&#41; + &#40;GET_RED&#40;back&#41; * beta&#41;&#41; / 255,
		&#40;&#40;GET_GREEN&#40;front&#41; * alpha&#41; + &#40;GET_GREEN&#40;back&#41; * beta&#41;&#41; / 255,
		&#40;&#40;GET_BLUE&#40;front&#41; * alpha&#41; + &#40;GET_BLUE&#40;back&#41; * beta&#41;&#41; / 255&#41;;
&#125;

void BitBltA&#40;unsigned long x,unsigned long y,unsigned long w,unsigned long h,unsigned long mag,const unsigned short *d, const unsigned char * m&#41;
&#123;
	unsigned char *vptr0;		//pointer to vram
	unsigned char *vptr;		//pointer to vram
	unsigned long xx,yy,mx,my;
	const unsigned short *dd;
	const unsigned char * mm;

	vptr0=&#40;unsigned char*&#41;pgGetVramAddr&#40;x,y&#41;;
	for &#40;yy=0; yy<h; yy++&#41; &#123;
		for &#40;my=0; my<mag; my++&#41; &#123;
			vptr=vptr0;
			dd=d;
			mm=m;
			for &#40;xx=0; xx<w; xx++&#41; &#123;
				for &#40;mx=0; mx<mag; mx++&#41; &#123;
					*&#40;unsigned short *&#41;vptr = alpha_blend&#40;*dd,*&#40;unsigned short *&#41;vptr,*mm&#41;;
					vptr+=PIXELSIZE*2;
				&#125;
				dd++;
				mm++;
			&#125;
			vptr0+=LINESIZE*2;
		&#125;
		d+=w;
		m+=w;
	&#125;

&#125;

It requires a separate mask, in this case it's just 8bit so you'll need to have appropriate arrays looking something like this:

Code: Select all

//Image size: (8,8)
const unsigned short bmp_shot_r[] =
{
	0x8000,0x8000,0x8000,0x8000,0x8000,0x8000,0x8000,0x8000,
	0x8000,0x8000,0x8000,0x8000,0x8000,0x8000,0x8000,0x8000,
	0x8000,0x8000,0x8000,0x8000,0x8000,0x8000,0x8000,0x8000,
	0x8000,0xd120,0xedc3,0xee43,0xff29,0xfff1,0xfff3,0x8000,
	0x8000,0xd120,0xedc3,0xee43,0xff29,0xfff1,0xfff3,0x8000,
	0x8000,0x8000,0x8000,0x8000,0x8000,0x8000,0x8000,0x8000,
	0x8000,0x8000,0x8000,0x8000,0x8000,0x8000,0x8000,0x8000,
	0x8000,0x8000,0x8000,0x8000,0x8000,0x8000,0x8000,0x8000
};

//Image size: (8,8)
const unsigned char mask_bmp_shot_r[] =
{
	0x0,0x0,0x0,0x0,0x0,0x0,0x0,0x0,
	0x0,0x0,0x0,0x0,0x0,0x0,0x0,0x0,
	0x0,0x0,0x0,0x0,0x0,0x0,0x0,0x0,
	0x0,0xff,0xff,0xff,0xff,0xff,0xff,0x0,
	0x0,0xff,0xff,0xff,0xff,0xff,0xff,0x0,
	0x0,0x0,0x0,0x0,0x0,0x0,0x0,0x0,
	0x0,0x0,0x0,0x0,0x0,0x0,0x0,0x0,
	0x0,0x0,0x0,0x0,0x0,0x0,0x0,0x0
};


//call as such: BitBltA(x,y,8,8,2,bmp_shot_r,mask_bmp_shot_r);

I also have code now set up to take 24bit bitmaps and produce the 16bit sprite & 8bit masks as above if anyone needs them (along with some extra stuff to print fonts from a bitmap organised like those shown .here

[Tychom]

As an aside, has anyone idea about how much static data can be held (i.e. how big the stack can be), without malloc i'm storing already upwards of 300k in bitmap & mask data..

[blackdroid]

well you know where userspace starts, and you have 24MB to play with, lots of pointers to use in case you worry about stack trashing.

[webjeff]

OK,

im seein some wierd results from your bitbltA function.

Here is my image and mask:
const unsigned short image[]={
0x7c00,0x7c00,0x7c00,0x7c00,0x7c00,0x7c00,0x7c00,0x7c00,0x7c00,0x7c00,0x7c00,0x7c00,0x7c00,0x7c00,0x7c00,0x7c00,
0x7c00,0x7c00,0x7c00,0x7c00,0x7c00,0x7c00,0x7c00,0x7c00,0x7c00,0x7c00,0x7c00,0x7c00,0x7c00,0x7c00,0x7c00,0x7c00,
0x7c00,0x7c00,0x7c00,0x7c00,0x7c00,0x7c00,0x7c00,0x7c00,0x6c04,0x6c04,0x6c04,0x6c04,0x6c04,0x6c04,0x6c04,0x6c04,
0x6c04,0x6c04,0x001f,0x001f,0x001f,0x001f,0x001f,0x001f,0x001f,0x001f,0x001f,0x001f,0x001f,0x001f,0x001f,0x001f,
0x001f,0x001f,0x001f,0x001f,0x001f,0x001f,0x001f,0x001f,0x001f,0x001f,0x001f,0x001f,0x001f,0x001f,0x001f,0x001f,
0x001f,0x001f,0x001f,0x001f,0x001f,0x001f,0x001f,0x001f,0x001f,0x001f,0x001f,0x001f,0x001f,0x001f,0x001f,0x001f,
0x001f,0x001f,0x001f,0x001f,
};

const unsigned short mask[]={
0x0,0x0,0x0,0x0,0x0,0x0,0x0,0x0,0x0,0x0,0x0,0x0,0x0,0x0,0x0,0x0,
0x0,0x0,0x0,0x0,0x0,0x0,0x0,0x0,0x0,0x0,0x0,0x0,0x0,0x0,0x0,0x0,
0x0,0x0,0x0,0x0,0x0,0x0,0x0,0x0,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,
0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,
0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,
0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,
0xff,0xff,0xff,0xff,
};


This is a 16 bit image, with red on top and blue on the bottom, im just tryin to mask out either color and its coming up all messed up, it works fine if I use bitblt, but not right using bitbltA (the function you posted above) any ideas??

Thanks
Jeff

[Tychom]

the mask array should be of type "const unsigned char []", not short. Other than that, your mask array is split 40-60% so you'll still see a bit of blue (if that's what you wanted then all's good :) )