Andrew Kesterson
5709dc160c
A drawing lasted exactly one frame. The verbs are immediate, they went to the back buffer, SDL double-buffers and the frontend never clears -- so the only way to keep a picture was to capture it with `SSHAPE` and install it as a sprite, which is what `examples/breakout/sprites/breakout.bas` spends two of its eight sprites doing. That was TODO.md section 9 item 9. The drawing verbs now render into a layer texture the frame composites under the text and the sprites. Draw once; it is there on every frame after. **Bracketed around the step phase, not around each verb.** One pair of `SDL_SetRenderTarget` calls a frame instead of one per `DRAW`, and it is also what makes `SSHAPE` read back what the program has just drawn rather than whatever the last frame left. **The layer is transparent where nothing was drawn.** It covers the whole window and composites underneath, so an opaque one would black out the frame the moment a program issued a single `DRAW`. And a fresh SDL target texture's contents are undefined, so it is cleared on creation -- skipping that puts uninitialised memory under the first frame's text and looks like a driver bug rather than a missing memset. **The line editor forced a wrinkle worth naming.** `akbasic_frontend_akgl_pump()` is called from two places with different answers to "is a render target current": the frame loop calls it between steps, and the sink's editor calls it from *inside* a step, borrowing a frame while it waits for a typed line. SDL refuses to present while a target is current, so the pump ends the layer, presents, and puts it back only if it was the one that ended it. `akgl_frontend` caught this -- it drives a REPL session, and it failed with "You can't present on a render target" the first time the brackets went in. This does not make a drawing *visible* on its own. The text layer still repaints every row it owns, opaque, every frame, and by default it owns the whole window; `WINDOW` shrinks it and that half was already fixed. The two together are what a picture needed, and the tests assert both -- a pixel still there a frame later with nothing redrawn, and a pixel below a shrunk text area surviving the text repaint. The second assertion wipes to a non-black colour first, because against black it could not tell a transparent layer from an opaque one. The tests found two of their own bugs on the way: `stop_runtime()` was not tearing the graphics backend down, so re-initialising it dropped a live texture on the floor; and a first draft called `begin()` before `start_runtime()`, which re-inits the backend, so the assertion read back off an orphaned render target and passed while proving nothing. Chapters 6 and 13 stop saying a drawing has to be redrawn every frame, because it does not. The batch-boundary tear stays documented -- it bites an `SSHAPE` capture, which matters much less now that capturing is not the only way to keep a picture. Both games still run clean. 111 with akgl, 110 without. Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01EwxGB6TdoVvZ11KQQME9cL
44 KiB
44 KiB