Latest 68K P96 Developer Documentation

Karlos · 06 February 2024, 17:18

Probably one for @ThoR

As the title suggests, I'm looking for the developer documentation for the latest 68K versions of Picasso96.

What I am actually interested to find out for now is if there are any functions in there for reading and adjusting output DAC parameters like brightness, contrast, gamma etc., or whether it's all just down to what you feed LoadRGB32().

alexh · 06 February 2024, 17:43

Have you tried here:

http://wiki.icomp.de/wiki/P96#Developer_support
http://wiki.icomp.de/wiki/P96_Driver_Development

pipper · 06 February 2024, 23:50

There is no direct P96 API for setting a gamma ramp. Maybe it could be done via "Features" in P96 (which is a way of exposing additional hw capabilities), but even if it was available, most VGA chips of that time didn't have a gamma ramp. You'd have to encode that into the palette.

Karlos · 07 February 2024, 01:11

Fixed point gamma it is then. For my use case, a linear interpolation of the form n.x^2 + (1-n).x (x in the range 0 - 1) gives a reasonable approximation for the "positive" side, and a similar interpolation between x and x^2 for the negative side, at least if my graphing calculator is telling me the truth.

06 February 2024, 17:18	#1
Karlos Alien Bleed Join Date: Aug 2022 Location: UK Posts: 4,165	Latest 68K P96 Developer Documentation Probably one for @ThoR As the title suggests, I'm looking for the developer documentation for the latest 68K versions of Picasso96. What I am actually interested to find out for now is if there are any functions in there for reading and adjusting output DAC parameters like brightness, contrast, gamma etc., or whether it's all just down to what you feed LoadRGB32().

07 February 2024, 01:11	#4
Karlos Alien Bleed Join Date: Aug 2022 Location: UK Posts: 4,165	Fixed point gamma it is then. For my use case, a linear interpolation of the form n.x^2 + (1-n).x (x in the range 0 - 1) gives a reasonable approximation for the "positive" side, and a similar interpolation between x and x^2 for the negative side, at least if my graphing calculator is telling me the truth. Last edited by Karlos; 07 February 2024 at 01:23.

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06 February 2024, 17:43	#2
alexh Thalion Webshrine Join Date: Jan 2004 Location: Oxford Posts: 14,354	Have you tried here: http://wiki.icomp.de/wiki/P96#Developer_support http://wiki.icomp.de/wiki/P96_Driver_Development

06 February 2024, 23:50	#3
pipper Registered User Join Date: Jul 2017 Location: San Jose Posts: 653	There is no direct P96 API for setting a gamma ramp. Maybe it could be done via "Features" in P96 (which is a way of exposing additional hw capabilities), but even if it was available, most VGA chips of that time didn't have a gamma ramp. You'd have to encode that into the palette.

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