Hunter

Hunter is an animated hunting scene program that depicts a figure firing a gun, with a projectile traveling across the screen to strike a bird in flight. The program uses PLOT and DRAW commands to render a ballistic trajectory line, then erases it using OVER 1 (XOR mode) to simulate motion. SOUND commands configure the AY chip with envelope and tone registers for gunshot and bird-call effects. After the shot sequence, the BORDER color is cycled through values 0–6 in a repeating loop to create a flashing effect before the program loops back to the start.

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Program Structure

The program is a single-scene animation that runs as a continuous loop. It can be broken into the following phases:

1. Setup (lines 10–60): Sets colors, draws a hunter figure using PRINT with OVER 1 overlays and a series of PLOTs for detail.
2. Bird drawing (lines 70–100): Plots a bird in flight as a small two-pixel-wide block at a fixed Y coordinate, sweeping from x=99 to x=244, then erasing the trailing pixel with OVER 1 to simulate movement.
3. Gun firing (lines 110–130): Draws a trajectory line with DRAW, pauses, then erases it with DRAW OVER 1. A SOUND command produces the gunshot.
4. Bullet/impact animation (lines 140–210): A loop moves a three-pixel vertical marker down the right side of the screen while playing a rising-pitch tone, simulating a falling bird.
5. Post-shot effects (lines 220–290): Additional SOUND calls followed by a BORDER color cycling loop (0–6, repeated 3 times) creating a flashing finale.
6. Loop and save (lines 300–310): Clears FLASH and BRIGHT attributes, then GO TO 10 to restart. Line 310 saves the program with autostart.

Graphics Techniques

The hunter figure at the left edge is constructed by layering characters using CHR$ 8 (cursor left) and OVER 1 to XOR-combine characters on screen — for example, printing "o" then overlaying "//" to form the gun or body shape. The same OVER 1 technique is used throughout to erase previously drawn graphics without clearing the whole screen, which is a standard technique for flicker-free animation on this platform.

The bird animation in lines 70–100 draws a 2×2 block of pixels at each x position and immediately erases the left column with OVER 1, leaving a leading two-pixel wide dot that travels across the screen. This gives the impression of a small bird in flight without storing sprite data.

The trajectory line (line 110) uses a single DRAW 218,148 from coordinate (26,24), spanning a large diagonal across the screen. It is erased with DRAW OVER 1;-218,-148 after a 4-frame pause, producing a brief visible shot line.

SOUND Register Usage

Several SOUND commands program the AY chip directly via register/value pairs. The key calls are:

Line	Registers set	Purpose
120	6,15; 7,7; 8,16; 9,16; 10,16; 12,16; 13,0	Gunshot sound — noise period, mixer, channel volumes, envelope period and shape
150	7,62; 8,15	Enables channels/noise for bird tone, sets channel A volume
180	0,i (i=50..100)	Sweeps channel A coarse tone register upward for a falling-pitch whistle effect
220	6,6; 7,7; 8,16; 9,16; 10,16; 12,56; 13,8	Second sound burst — impact/thud with different envelope settings
240	8,0; 9,0; 10,0	Silences all three channels by zeroing their volume registers

Notable Techniques

• OVER 1 for erasure: Used consistently instead of redrawing over background color, preserving other screen content.
• CHR$ 8 cursor repositioning: Allows multiple characters to be overlaid at the same screen cell within a single PRINT statement chain, building composite glyphs.
• Rising tone sweep: The loop at lines 160–200 increments the AY tone register from 50 to 100 with a PAUSE 3 between steps, creating a smooth pitch glide synchronized with the falling-bird pixel animation.
• BORDER flash finale: Lines 250–290 cycle BORDER through colors 0–6 three times with short pauses, producing a rapid color flash effect without using the FLASH attribute — this avoids the 50Hz cell-level flashing limitation and gives a full-screen color burst.
• Pixel-level bird motion: The bird sweep uses individual PLOT calls rather than DRAW or PRINT, giving sub-character pixel precision for the animation path at y=172/171.

Potential Issues

Line 100 ends with NEXT x after the bird sweep, but the variable x is reused in line 250 for the BORDER flash loop without being re-declared — this is harmless since LET is not required before FOR, and each FOR resets the variable. The falling-bird animation in lines 170–200 moves the marker downward (y decrements by 3 each iteration) starting from y=172, ending near y=22 after 50 iterations, which correctly maps the bird falling off screen.