OP scaled bitmap

[swapd0]

How do I calculate the correct value of REMAINER field in a vertical scaled object?

 

I've tried to put it to zero, use the same value as the VSCALE field, but all of them have some issues. Some times the OP draw more scanlines(extra scan line with random pixels), or it draws first scan line bigger than the others.

 

 

Edited December 12, 2019 by swapd0

[jguff]

22 hours ago, swapd0 said:

How do I calculate the correct value of REMAINER field in a vertical scaled object?

 

I've tried to put it to zero, use the same value as the VSCALE field, but all of them have some issues. Some times the OP draw more scanlines(extra scan line with random pixels), or it draws first scan line bigger than the others.

 

 

" Some times the OP draw more scanlines(extra scan line with random pixels) "

 

Are extra scanlines drawn before your bitmap, or after your bitmap?

[swapd0]

The extra scanline it's at the bottom of the bitmap, it's drawing one extra scaline and it's drawn scaled.

 

The other issue it's that the first scanline it's drawn two times.

 

[jguff]

Unsure of your experience with Jaguar programming.

1) Have you successfully displayed other image data in scaled fashion?

2) Successfully displayed other image data in non-scaled fashion?

 

 

[swapd0]

1. Yes but if it's scaled all images have the same issue.

2. of course.

 

 

[jguff]

"How do I calculate the correct value of REMAINER field in a vertical scaled object?"

 

Do you need to calculate REMAINDER bits, or just initialize REMAINDER bits?

 

My understanding, from a version of the Software Reference, is:
...that you initialize the REMAINDER bits when create object list and when you recreate the object list after every vertical blank.
...the hardware updates this on a per scanline basis, in between vertical blanks.

 

[LinkoVitch]

It's been a LONG time since I looked, but IIRC the Scaled objects have a bug.. sorry, feature   Which is the random extra scan line you see.  I *think* the solution to this is to add a blank line to the bottom of your source object.

 

Sorry I cannot help with the remainder calcs, I haven't looked into those yet

[+CyranoJ]

Yep, its 'featured' - just pad an extra blank line at the top and bottom of the image  

[swapd0]

Cool, more wasted cycles drawing nothing.

[swapd0]

I've done some testing and I think that this is the best way to draw scaled bitmaps without wasting some cycles drawing an extra scan line (scaled), and without leaving an empty scan line in the bitmap.

 

1. always decrement object height by one (even if y scale it's $20)

2. set remainder = scale y

 

I haven't done many test with smaller objects (y scale < $20) but for now it looks ok.