Scale Image with DataTypes?

[AGS]

Hi,

is it possible to make an Image smaller with Datatypes? If yes, how?

thanks,
ags

[thomas]

Only in OS 3.9 and above there is PDTM_SCALE.

But if you read the bitmap from the datatype anyway, you can as well use BitMapScale in graphics.library.

[AGS]

Great idea, thank you. Now, what are these for:

	    bsa_XSrcFactor:bsa_XDestFactor - equivalent to the ratio
	        srcWidth:destWidth, but not necessarily the same
	        numbers.  Each must be in the range 1..16383.
	    bsa_YSrcFactor:bsa_YDestFactor - equivalent to the ratio
	        srcHeight:destHeight, but not necessarily the same
	        numbers.  Each must be in the range 1..16383.

Do I need them? I cannot see why.


PS: And is it possible to get the filetype with datatypes, i.e. if it's music or graphics?

[thomas]

Originally Posted by AGS

Do I need them?

Yes.

I cannot see why.

Because the documentation says so?

Your bitmaps might be bigger than the area you want to scale, therefore the factors determine by which factor scaling is done. For your special case X*Factor = *Width and Y*Factor = *Height.

PS: And is it possible to get the filetype with datatypes, i.e. if it's music or graphics?

If you want to restrict loading to a certain type, you can set DTA_GroupID in NewDTObject.
If you want to load every type of file and then determine what it is, you can GetDTAttrs(DTA_DataType).
If you want to find out what type a file is without loading it, ObtainDataType is the function to use.

[AGS]

I don't get it. I think I just do it the way the docu says. But if anyone could describe me this, it would also be good.

[AGS]

Ah, what if I want to scale the image while keeping aspect ratio?

[AGS]

Originally Posted by thomas

Yes.
For your special case X*Factor = *Width and Y*Factor = *Height.

I don't understand what the asterisks in front of Width and Height mean. Please could you explain or write the formulas more detailed?

[thomas]

XSrcFactor = SrcWidth, YSrcFactor = SrcHeight, same for Dest.

[AGS]

Okay, everything works fine now.

ps: even keeping aspect ratio!

[AGS]

I noticed that sometimes (seldom) the scaled image is slightly bigger than the available space and/or a one pixel border of some other color is to the right. can you see why? this is my aspect-ratio calculation:

.scale		; aspect ratio

		;// Calculate new size
		;if((containerw_d2 - picwidth_d4) > (containerh_d3 - picheight_d5)) {
			// use height
			;s = containerh_d3 / picheight_d5;
			;nw = round(picwidth_d4 * s);
			;nh = containerh_d3;
		;}
		;else { // Use width
			;s = containerw_d2 / picwidth_d4;
			;nw = containerw_d2;
			;nh = round(picheight_d5 * s);
		;}

		sub.w	d4,d2
		sub.w	d5,d3
		cmp.w	d2,d3
		bgt	.use_width

		movem.w	oxO_width(a3),d2/d3
		move.w	d3,d2
		mulu.w	d4,d2

		move.w	d5,d6
		lsr.w	#1,d6
		add.w	d6,d2

		divu.w	d5,d2
	
		bra	.center_scaled

.use_width	movem.w	oxO_width(a3),d2/d3
		move.w	d2,d3
		mulu.w	d5,d3
		
		move.w	d4,d6
		lsr.w	#1,d6
		add.w	d6,d3

		divu.w	d4,d3

.center_scaled	; new width and height now in d2 and d3

[thomas]

I don't understand your code. This is how I would do it:

new_w = max_w
new_h = old_h * max_w / old_w
if new_h > max_h then
	new_h = max_h
	new_w = old_w * max_h / old_h
endif