Display HAM image in Blitz - left edge fringing?

[Marle]

Hiya,

I'm trying to display a HAM image which works but unlike Multiview when I view the image, I am getting fringing on the left edge, when I view the exact same image with Multiview, no fringing on the left edge, so I'm a bit confused where I am going wrong.

Any ideas?

The first image is the result of the below blitz code, the second is Multiview.

Please note the image shown is not mine, I am just experimenting before I start painting my own backdrops. Many thanks!

Vicky

WBStartup
DEFTYPE.w

imagew = 455
displayw = 320

BitMap 0,imagew,256,6
LoadBitMap 0,"school-ham.iff",0

InitCopList 0,44,256,$6 + $80 + $10,8,32,0

VWait 100

BLITZ

CreateDisplay 0
DisplayPalette 0,0
DisplayBitMap 0,0,0,0

While Joyb(0)=0
  VWait
Wend

QAMIGA

Free Palette 0
Free BitMap 0


End

[thomas]

The image is a few pixels wider than the screen. Your program seems to cut them off at the left while Multiview cuts them at the right edge.

You should get the same result in Multiview if you move the mouse pointer against the right border so that the screen scrolls a bit to the left.

[Marle]

Thanks thomas, yes it does seem the case I didn't see that myself until I looked at the screenshots, hard to tell when I was working on it. I was experimenting panning a HAM bitmap but unfortunately you do get fringing doing that it seems, I would have thought the DisplayBitmap 0,0,0,0 would have ensured the left edge of the image was at the leftmost point but I'll experiment with a 320 wide bitmap.

Thanks!

[Marle]

Ok I tracked it down, it appears to be to do with having smooth scrolling enabled as even when I cropped the image to 320x256 it still was fringing on the left edge.

Disabling smooth scrolling seemed to work. ($86 instead of $96 for the copper list options)

[earok]

With Time Gal we had an issue where there was a slight artifacting on the left edge (to do with the greyscale palette that was shared between every frame of the HAM animation).

We fixed it when we reused the engine for Road Avenger by simply displaying a black sprite on the left edge of the screen.

If you wanted to scroll HAM you could maybe cover up the left side with a black sprite the same as what we did. If the black sprite is 16 pixels wide it should (not totally guaranteed) be wide enough to cover up any artifacts on the left.