Debug80 Docs

Glimmer Book 1 — Reactive Programming for Z80 Games99

Exercise Notes ​

Chapter 1: The Shape of a Game ​

The runtime scans the cleared framebuffer before it runs the reactive blocks, so the first scan is blank. DrawDot then plots (3,3). Its change bit clears at frame end, but the framebuffer keeps the pixel, so the second scan displays the dot without another call to DrawDot.

Chapter 2: First Light ​

The seven presses advance through green, yellow, blue, magenta, cyan and white, then wrap to red with Colour = 1. The eighth press advances to green with Colour = 2.

Chapter 3: State ​

DotX begins with its change bit set, so DrawBeacon runs at startup. Score begins with its bit clear, so ShowScore waits for the first score change. Declaring state Score : word changed makes the initial zero render as 000000.

Chapter 4: Pulses and Bindings ​

A rising binding moves once when the key first goes down; holding it produces no further pulses until the key is released and pressed again. A held period 8 binding fires immediately and then repeats, which suits continuous movement. Home represents one action per press, so rising avoids repeating the reset while the key remains down.

Chapter 5: Compute, Effect, Render ​

On frame N, Increase stores 1 in Count. Because Count also feeds the compute phase, which has already run, Glimmer defers that change as one unit. On frame N+1, DeriveBar stores 0 in BarLen, then the render phase writes the new digit and redraws the bar. The visible count and its derived bar therefore remain together.

Chapter 6: The 8x8 Matrix Profile ​

Row 2 begins eight bytes after Framebuffer because each row occupies four bytes. At x=5 the mask is %00000100 ($04). Yellow uses red and green, so the mask is ORed into row 2's red byte at offset 8 and green byte at offset 9. The blue byte at offset 10 remains unchanged.

Chapter 7: Time ​

Blink first fires on frame 5 and Fall on frame 24. Their first shared expiry is the least common multiple of 5 and 24, frame 120.

Chapter 8: Motion Curves ​

Entry 31 of Curve_Glide is 4, so CometX becomes 4. The values repeat for longer runs toward the destination, which means the position changes less often and the comet slows as it arrives.

Chapter 9: Shapes, Sound and Displays on the Board ​

The four rows are $40, $E0, $40 and $40:

text
.X.  -> 01000000
XXX  -> 11100000
.X.  -> 01000000
.X.  -> 01000000

Chapter 10: Arrays and Layout Types ​

Picture reserves eight bytes and uses one change bit. The flag belongs to the array as a whole, so a write to any row raises the same Picture change and DrawCanvas rebuilds all eight rows.

Chapter 11: Dependency Reports and Debugging ​

The store changes the Marks byte, but the missing updates Marks declaration leaves its change bit clear. ShowMarks therefore receives no trigger. The repair is:

text
effect PaintPixel
    on Paint
    updates Picture, Marks

Chapter 12: Routines, Parts and Imports ​

A part contributes Glimmer declarations to the same program and namespace, which suits reactive blocks that use its facts and pulses. An import brings in a hand-written AZM module with an explicit register interface. The @ prefix exports an assembly label so code outside that module can call it.

Chapter 13: Cards ​

The GO press occurs while Splash is still the active card. It raises both AnyKeyP and HitP, but Playing's ScorePoint block is gated off. CurrentCard changes for the following frame, after both pulses have cleared, so the new round begins at zero.