[VCS] Gopher2600 Preview 3 0.40 23/02/2025

Atari 2600 Emulator: Gopher v0.34 Preview 3 23/02/2025

(...)In this preview I have changed the output value of "black" as produced by NTSC Colour-Lum value $00. For PAL and SECAM there are more values that produce "black" and this applies to them too. The purpose of this change is to make it the same value of the "black" produced by VBLANK.

Without going into too much detail, the purpose of this change is to ensure that both types of black (the one produced by VBLANK and the one produced by Colour-Lum $00) are affected by the brightness/contrast controls equally, which is what can be observed on real hardware.(...)

Other Changes

• Corrected detected of "PAL60" in filename

• This controls the specification of the emulated television

• DPC (Pitfall II) fingerprinting

• The detection for DPC is based purely on size of the ROM file
• Problem identified in #36

• DPC Random Number Generator

• Corrected random number algorithm to more closely match DPC patent
• Pumped on every cartridge access and not just on 'non-volatile' access

• ARM Timers

• ARM timers more efficiently updated
• Small improvement in performance

• ELF Performance

• Small efficiency improvements

Atari 2600 Emulator: Gopher v0.34 Preview 2 17/02/2025

...In the image you will notice that the rim around the screen is not tinted by blue because it is illuminated by the screen, which has a different predominant colour.

This is a second preview release of v0.40.0. I'm still not satisfied with what I am now referring to as the new colour model so I'm still holding off making a non-preview release. And I still want to emphasise that the colours are not 'final' or fully understood.

Colour Models

The changes to the new colour model are as follows

• NTSC colour burst
  • Previously a phase adjustment would cause the burst to change very slightly, which it shouldn't. The burst is now fixed in all instances.
• IQ and UV values are no longer scaled by Y
• Contrast adjustment now uses a grey level of 7.5%
  • colour-lum of 0 is set to 7.5% grey

Other Changes

• ARM

• Small performance improvement during cycle accumulation
  • Separation of integer and fractional parts of a cycle count now uses SIMD instructions

• Patch Files

• Missing patch file is no longer a fatal error
• Patch file given on the command line is not assumed to be in the patches directory of the configuration directory.
  • The path given on the command line is now an absolute path

• SDL Audio

• Small performance improvement caused by calling sdl.AudioQueue() less frequently
• Queue management now slows the sample rate when queue is running low
  • This should result in fewer audio buffer underruns

Atari 2600 Emulator: Gopher v0.34 Preview 13/01/2025