Magnify12

This program magnifies text characters to a large size by sampling each pixel of a source character using the POINT command and printing a chosen fill character in its place, effectively scaling up letters for banner-style output. It supports one or two lines of text and offers several display modes: a preset “relief” style using light or dark shading, or a user-selected pair of background and text characters drawn from a built-in set of block graphics (spaces, UDGs, and Spectrum block characters). The magnified output is sent simultaneously to the screen with PRINT AT and to a printer with LPRINT, using TAB positioning for column alignment. Characters are examined column-by-column (outer loop) and row-by-row (inner loop), with POINT reading the pixel state at coordinates derived from the character cell rendered at the bottom of the screen at rows 20–21.

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Program Analysis

Program Structure

The program is divided into three broad phases: setup (lines 10–170), character selection (lines 180–400), and the main magnification loop (lines 410–800). Setup asks for the number of lines (1 or 2) and whether a “relief” style preset is desired. Character selection presents a menu of four block-graphic options for background and text fill, with an option to supply a custom character. The magnification phase iterates over each character of the input text, renders it in small form at the bottom of the screen, samples it with POINT, and prints a magnified version using the chosen fill characters.

Key Data Structures

• A$(2,255) — stores up to two lines of input text, each up to 255 characters.
• L$(10) — a 10-element string array used as a character lookup table; positions 1–4 hold space and three block graphics, position 5 is a user-supplied background character, position 6 a user-supplied text character, and positions 7–10 hold additional half-block graphics set at line 510.
• D(2) — two-element array indexing L$: D(1) selects the background fill character, D(2) selects the text fill character.
• C(2) — stores the column center coordinates for each of the two possible lines of text.

Magnification Technique

The core of the program is the subroutine at line 680. Each source character is printed invisibly at the bottom of the screen (rows 20–21 via lines 600–620) so that its pixel bitmap is available for sampling. The subroutine then uses five nested loops to walk every pixel in the 8×8 character grid (columns C 0–7, rows R 0–7), reading each pixel with POINT (C, R+B*8). A non-zero POINT result sets SWITCH=2 (text character); zero sets SWITCH=1 (background character). Each source pixel is then reproduced as a block of M×M fill characters on screen, where M=4/LINES (4 for one line, 2 for two lines).

Coordinate Calculation

The screen position for each magnified pixel block is computed as follows:

• Row: RCOOR = ROW - (M/2*8) + (C*M) + N — ROW is fixed at 11 (center of screen); column index C of the source character maps to the vertical axis of the magnified output (characters are rendered column-first), and N iterates within the M-high block.
• Column: CCOOR = C(B+1) - (M/2*8) + (R*M) + L — C(B+1) is the horizontal center for line B; source row R drives the horizontal axis of the output.

This column-major traversal of source pixels (outer loop on C, inner on R) means the character is effectively rotated 90°; the coordinate formula compensates so the output appears correctly oriented.

Dual Output

Line 780 uses PRINT AT RCOOR,CCOOR for screen display (skipped for single-line mode at line 770), while line 790 always executes LPRINT TAB CCOOR to send output to a printer. The single-line mode bypasses the screen PRINT entirely (relying solely on LPRINT), which appears to be intentional given the variable is named LINES.

Character Set Initialization

Lines 500–510 populate the L$ lookup table using a mix of a space character, UDG characters \a and \b, and Spectrum block graphics \::, \ ', \. , \':, \:.:

Index	Content	Typical appearance
1	space	blank
2	UDG \a	user-defined graphic A
3	UDG \b	user-defined graphic B
4	\:: (█)	full block
5	user input	custom background
6	user input	custom text
7	\ ‘ (▝)	top-right quarter block
8	\. (▖)	bottom-left quarter block
9	\’:(▛)	three-quarter block
10	\:. (▙)	three-quarter block (alt)

Relief Style Mode

When the user presses 7 (light relief) at line 140, D(2) is set to 8 (the ▖ block graphic); pressing 9 (dark relief) at line 150 sets D(2) to 10 (▙). In both cases D(1) is set from VAL D$ at line 160, yielding 7 or 9 respectively, selecting the complementary quarter-block character. This creates a subtle raised or embossed appearance in the magnified output.

Notable Idioms and Anomalies

• Line 340 uses PI as a column argument to PRINT AT; PI evaluates to approximately 3.14159, which truncates to 3, placing the prompt at column 3. This is an unusual use of a floating-point constant in place of an integer literal.
• Line 270’s PRINT AT 11,0,,: uses the comma-comma syntax to reset attributes without printing text, followed by a colon to continue on the same logical line — a compact attribute-clearing trick.
• The duplicate check at line 300 (IF D(1)=D(2) AND D(1)<>5) prevents choosing the same built-in character for both background and text, but allows both to be 5 (custom input), which would result in identical fill and no visible output.
• Line 160 is reached only in the relief branch (lines 140–150 fall through); if neither 7 nor 9 was pressed and D$ is not a digit, VAL D$ will return 0, causing D(1)=0 and a subscript error when L$(0,1) is accessed.
• INK 9 at line 630 selects “transparent” ink on the TS2068, making the small source characters at the bottom of the screen invisible to the user while still being readable by POINT.