Tandy: Implement CRTC-based display shifting (R2 & R7 registers) #6419
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- Replace frame-based calibration system with timer-based approach - Replace fixed scaling constants with dynamic video mode-aware calculations - Reduce unnecessary vid_update_display_offset() calls by filtering registers - Introduce dynamic horizontal/vertical scaling calculations - Update rendering pipeline to use dynamic display parameters
…riable/function naming
…er clock width calculation and remove vid_get_char_width()
…amp crtc[7] position to valid range and use calibrated baseline_vsyncpos for vsync comparison to avoid display issues when overscan in enabled
- Apply vsync_offset only during the vertical retrace period for a more accurate result - Change the calculation of displine_offs and remove redundant checks around rendering calls - Remove unnecessary clamping logic for crtc[7] - Remove a hack from the previous commit by correctly triggering VSYNC processing when the vertical counter matches the actual crtc[7]
…he rendering functions
…TC register writes
Member
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I'm getting this warning now: |
Contributor
Author
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Sorry about that - I didn't get any warnings when I built it on my end. 481 511 That should make it clear to the compiler. |
Member
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Committed that and it does fix the warnings, thanks! |
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Summary
This PR adds support for shifting the display position using the CRTC's Horizontal Sync Position (R2) and Vertical Sync Position (R7). This enables the so-called the “screen shake” effect seen in many Sierra games, achieved by dynamically rewriting the specified registers on the fly.
kq1_test.webm
A baseline calibration is used to distinguish between a game setting the initial screen position and a game intentionally shifting the screen for effect. After a video mode is set, the centered sync positions are stored as a reference. Every write to R2 or R7 triggers a calculation of the difference from the stored baseline.
Values outside the documented limits of these registers are not fully emulated:
R4 >= R7 >= R6), but this only affects software that deliberately pushes the CRTC beyond spec to create special visual effects (for example - Area 5150)Here's a test (within the documented range for R7) across three different modes: 80-column text, 320x200x4, and 320x200x16.
basica_test.webm
All other modes available through BASICA have been tested as well.
640x200x16 for Tandy Video II (SL/2) was tested in a game that supports this mode.
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References
Provide links to datasheets or other documentation that helped you implement this pull request.