Changing sprite images in long display lists

phx · 12 March 2016, 18:25

To change the image of a sprite (channel) you will just point its SPRxPT to a different display list with the new image.

But let's assume we have a sprite display list which contains multiple images at different locations of the screen. Then this method becomes annoyingly uncomfortable. Or am I missing something?

Having to copy the current bitmap image for every section in this sprite display list seems stupid. So I wonder if it is possible to set SPRxPT to a new display list in the middle of the display? But my feeling is that you can only write SPRxPT during Vertical Blank...

Toni Wilen · 12 March 2016, 19:20

You can modify SPRxPT but because Agnus loads next sprite control words after previous sprite has ended (not when new sprite starts), first new fetch from new SPRxPT would be first line of sprite data, not control worlds which most likely is not what you wanted.

It will work if you update SPRxPOS/SPRxCTL with new coordinates and SPRxPT with pointer to new sprite data.

There is also another option: if you don't want to copy coordinates, you can force control wold reload by setting sprite's vertical _stop_ to current (or later) vertical position. Agnus will think previous sprite ends when stop matches (even if it was already ended or is still active!) and reloads next control worlds and continues normally.

Check also http://eab.abime.net/showthread.php?t=81866

phx · 12 March 2016, 20:13

Thanks!
Sorry, completely missed that thread. What a coincidence!

12 March 2016, 18:25	#1
phx Natteravn Join Date: Nov 2009 Location: Herford / Germany Posts: 2,500	Changing sprite images in long display lists To change the image of a sprite (channel) you will just point its SPRxPT to a different display list with the new image. But let's assume we have a sprite display list which contains multiple images at different locations of the screen. Then this method becomes annoyingly uncomfortable. Or am I missing something? Having to copy the current bitmap image for every section in this sprite display list seems stupid. So I wonder if it is possible to set SPRxPT to a new display list in the middle of the display? But my feeling is that you can only write SPRxPT during Vertical Blank...

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12 March 2016, 19:20	#2
Toni Wilen WinUAE developer Join Date: Aug 2001 Location: Hämeenlinna/Finland Age: 49 Posts: 26,517	You can modify SPRxPT but because Agnus loads next sprite control words after previous sprite has ended (not when new sprite starts), first new fetch from new SPRxPT would be first line of sprite data, not control worlds which most likely is not what you wanted. It will work if you update SPRxPOS/SPRxCTL with new coordinates and SPRxPT with pointer to new sprite data. There is also another option: if you don't want to copy coordinates, you can force control wold reload by setting sprite's vertical _stop_ to current (or later) vertical position. Agnus will think previous sprite ends when stop matches (even if it was already ended or is still active!) and reloads next control worlds and continues normally. Check also http://eab.abime.net/showthread.php?t=81866

12 March 2016, 20:13	#3
phx Natteravn Join Date: Nov 2009 Location: Herford / Germany Posts: 2,500	Thanks! Sorry, completely missed that thread. What a coincidence!

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