Titlemaker

Titlemaker is a TS2068 BASIC subroutine that renders user-entered text at double size by exploiting the POINT function to read pixel data from a string printed off-screen at line 21. For each pixel set in the standard-size text, the routine uses nested loops to PLOT a 2×2 block at a calculated screen position, effectively doubling both horizontal and vertical resolution. The title is centered horizontally using a formula based on the string length and a fixed X origin of 128. Input is validated to reject empty strings and strings longer than 16 characters before rendering.

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Program Structure

The program is organized into a short main loop and a single subroutine:

1. Lines 10–60: Main loop — clears the screen, accepts input, validates length, calls the rendering subroutine, then repeats.
2. Lines 70–170: The core double-size rendering subroutine.
3. Line 180: A SAVE statement with autostart at line 10.
4. Line 190: A REM comment describing the program and its author.

Input and Validation

Lines 20–40 handle user input. An empty string causes a loop back to line 20 via IF t$="" THEN GO TO 20. The string is copied to y$ at line 30, and if its length exceeds 16 characters, line 40 sends control back to line 20. The 16-character limit is practical: each character renders as 16 pixels wide when doubled, so 16 characters fills 256 pixels — exactly the screen width.

Rendering Technique

The double-size effect is achieved without machine code by using the built-in POINT function as a pixel-level reader. At line 80, the title string y$ is printed at row 21 (the bottom line of the display), placing it in a region used as a temporary pixel buffer. The outer loops then scan each pixel of the rendered text:

• a (line 90): iterates rows from 7 down to 0 — the 8 pixel rows of a character cell.
• b (line 100): iterates columns from 0 to 8 * LEN y$ - 1, covering every pixel column across all characters.
• Line 110 uses POINT (b, a) to test whether that pixel is lit. The coordinate origin of POINT is at the bottom-left of the screen, so row 21 characters correspond to a values 0–7.
• If the pixel is set, inner loops c and d (lines 120–150) each run 0 to 1, and PLOT places a 2×2 block of pixels at the scaled destination.

Coordinate Calculations

The destination X coordinate in line 140 is x - (8 * LEN y$) + 2*b + c, where x = 128. This centers the doubled text: 8 * LEN y$ is half the total pixel width of the doubled string (since each source pixel becomes 2 pixels wide), so subtracting it from 128 (the horizontal midpoint) gives a left-aligned start that results in centering. The Y coordinate is y + 2*a - d, where y = 157, placing the doubled title roughly in the upper-center of the screen and scaling vertically by 2.

Cleanup and Reuse

Line 170 uses PAUSE b as a brief delay (the value of b after the loop exits is 8 * LEN y$, providing a pause proportional to the string length). The PRINT AT 21,0,; then clears the temporary buffer line before returning, leaving the double-size plot visible. The routine is structured as a proper subroutine (ending with RETURN), so it can be called from external programs.

Notable Techniques and Anomalies

• Using POINT to read back pixels that were just printed is an elegant workaround for lack of direct character font data access in BASIC.
• The variable y$ is redundant — t$ is copied to y$ at line 30 but could be used directly; this may be a remnant of earlier development.
• The PAUSE b at line 170 reuses the loop variable rather than a literal, giving a variable-length pause as an unintentional but functional side effect.
• The centering formula assumes the doubled text should be horizontally centered at pixel column 128. This works for strings up to 16 characters; longer strings are rejected by the input validation.
• The loop at line 90 iterates a from 7 down to 0. Since POINT uses screen coordinates with Y=0 at the bottom, a=0 is the bottom pixel row of the character and a=7 is the top — the downward iteration produces correct top-to-bottom rendering in the doubled output due to the 2*a scaling.