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#241 Info-topics support on the debugger. Was: overlay for raster
The VDP implementation of openMSX certainly knows the current pixel being drawn by the rasterizer at a given moment. It would be useful to have an overlay (a toggle, like toggle_scc_viewer) to show the coordinates of the pixel currently being drawn by the VDP.
Due to the speed, this overlay will of course only be useful when running openMSX on step-by-step while debugging. This will help the programmer to:
- Know when certain events will be triggered (vblank interrupt, line interrupt)
- Debug why a sprite drawing glitch is happening (usually because of concurrent VRAM writes while the rasterizer is at a that address)
- Debug splitscreen glitches
This is already possible. I mean this request doesn't need changes on the c++ side, someone only needs to write a Tcl script to show the overlay.
The required information can be obtained via the following info topics (machine_info <topic-name>):
-VDP_frame_count
-VDP_cycle_in_frame
-VDP_line_in_frame (*)
-VDP_cycle_in_line (*)
-VDP_msx_y_pos (#)
-VDP_msx_x256_pos (#)
-VDP_msx_x512_pos (#)
(*) Redundant, these could be calculated from VDP_cycle_in_frame
(#) Redundant, these could be calculated from VDP_cycle_in_frame plus 'set adjust' information.
Use 'help machine_info <topic-name>' for more details on a certain topic.
(Use 'machine_info' (so without any parameters) to get a list of all available topics. Or 'openmsx_info' for topics that are not
msx machine specific).
I'm not convinced an overlay is the best way to go. We also don't make overlays for e.g. the Z80 registers. Instead such 'debuggables' are shown in the debugger. It might be a good idea to also show info topics in the debugger.
BTW the difference between debuggables and info topics is that debuggables are always a byte array while info topics only have a single value per topic (but they are not necessarily limited to a byte, some are even strings).
I didn't knew about the info-topics. If the debugger could support those, this could be even better than the overlay idea.