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f18a fpga vdp 9918a 9928 video hardware mods upgrade updates

577 replies to this topic

#576 matthew180 OFFLINE  

matthew180

    River Patroller

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  • Location:Castaic, California

Posted Thu May 11, 2017 3:28 PM

In the original color mode, the pattern pixel ('0' or '1') selects between one of two colors from the color table.  If either color value from the color table is zero, then the backdrop color is used (i.e. the pixel is transparent).  This is why the 9918A has color black as the second color (see pg. 2-17 in the 9918A data sheet), because you need a way to differentiate between transparent and a color.  If you want to use sixteen *colors* without a transparent, then color zero needs to be your black and you need to set the backdrop color (via VR7) to black so that the zero-index transparent pixels show as black.

 

Using the palette above in post #570, just set VR7 to >x0 (the low nibble needs to be 0) and it should work as expected.



#577 InsaneMultitasker OFFLINE  

InsaneMultitasker

    Stargunner

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Posted Thu May 11, 2017 7:28 PM


Using the palette above in post #570, just set VR7 to >x0 (the low nibble needs to be 0) and it should work as expected.

Setting VR#7 like you suggested seems to have done the trick.  The palette is working now, and I've been able to test a few routines against it!  The index magic is still a bit of a mystery to me ;)   Thank you and Rasmus for helping me resolve this!



#578 matthew180 OFFLINE  

matthew180

    River Patroller

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Posted Thu May 11, 2017 8:29 PM

I'll see if I can get something written up that explains the color selection.







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