andrew/libakgl
1
0
Fork 0
Code Issues Pull Requests Actions Packages Projects Releases Wiki Activity

Measure rendered text without drawing it

Browse Source 
akbasic needs the advance width of one character cell to build a terminal-style
text surface, and the wrapped size to know where a string crosses the right
margin. akgl_text_measure and akgl_text_measure_wrapped report both over
TTF_GetStringSize and TTF_GetStringSizeWrapped; neither needs a renderer, so
this half of the text subsystem is testable without the offscreen harness.

A negative wrap length is refused with AKERR_OUTOFBOUNDS: SDL_ttf reads it as a
very large unsigned width and quietly stops wrapping, which would return a
measurement that is wrong rather than an error the caller can see.

Also fixes akgl_text_loadfont, which checked name twice and passed an unchecked
filepath to TTF_OpenFont (TODO item 39).

The fixture font is a 10 KB monospaced ASCII subset of Liberation Mono, renamed
because "Liberation" is a Reserved Font Name; see
tests/assets/akgl_test_mono.LICENSE.txt. Monospaced so the suite can assert
width("AAAA") == 4 * width("A") rather than hardcode glyph metrics.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
This commit is contained in:
Andrew Kesterson
2026-07-31 06:55:25 -04:00
parent 5f03475e0f
commit 17e6e04c79
7 changed files with 477 additions and 1 deletions
Download Patch File Download Diff File Expand all files Collapse all files

45
src/text.c
View File

@@ -16,7 +16,7 @@ akerr_ErrorContext AKERR_NOIGNORE *akgl_text_loadfont(char *name, char *filepath
PREPARE_ERROR(errctx);
FAIL_ZERO_RETURN(errctx, name, AKERR_NULLPOINTER, "Null font name");
FAIL_ZERO_RETURN(errctx, name, AKERR_NULLPOINTER, "Null filepath");
FAIL_ZERO_RETURN(errctx, filepath, AKERR_NULLPOINTER, "Null filepath");
font = TTF_OpenFont(filepath, size);
FAIL_ZERO_RETURN(errctx, font, AKGL_ERR_SDL, "%s", SDL_GetError());
FAIL_ZERO_RETURN(
@@ -64,3 +64,46 @@ akerr_ErrorContext AKERR_NOIGNORE *akgl_text_rendertextat(TTF_Font *font, char *
SDL_DestroySurface(textsurf);
SUCCEED_RETURN(errctx);
}
akerr_ErrorContext AKERR_NOIGNORE *akgl_text_measure(TTF_Font *font, char *text, int *w, int *h)
{
PREPARE_ERROR(errctx);
FAIL_ZERO_RETURN(errctx, font, AKERR_NULLPOINTER, "NULL font");
FAIL_ZERO_RETURN(errctx, text, AKERR_NULLPOINTER, "NULL text string");
FAIL_ZERO_RETURN(errctx, w, AKERR_NULLPOINTER, "NULL width destination");
FAIL_ZERO_RETURN(errctx, h, AKERR_NULLPOINTER, "NULL height destination");
// A zero length means "the string is null terminated", not "the empty
// string" -- an empty text measures 0 wide and one line high.
FAIL_ZERO_RETURN(
errctx,
TTF_GetStringSize(font, text, 0, w, h),
AKGL_ERR_SDL,
"%s",
SDL_GetError());
SUCCEED_RETURN(errctx);
}
akerr_ErrorContext AKERR_NOIGNORE *akgl_text_measure_wrapped(TTF_Font *font, char *text, int wraplength, int *w, int *h)
{
PREPARE_ERROR(errctx);
FAIL_ZERO_RETURN(errctx, font, AKERR_NULLPOINTER, "NULL font");
FAIL_ZERO_RETURN(errctx, text, AKERR_NULLPOINTER, "NULL text string");
FAIL_ZERO_RETURN(errctx, w, AKERR_NULLPOINTER, "NULL width destination");
FAIL_ZERO_RETURN(errctx, h, AKERR_NULLPOINTER, "NULL height destination");
// SDL_ttf takes the wrap width as an int and reads a negative one as a
// very large unsigned width, which silently disables wrapping instead of
// reporting anything. Refuse it here rather than return a wrong measurement.
FAIL_NONZERO_RETURN(
errctx,
(wraplength < 0),
AKERR_OUTOFBOUNDS,
"Wrap length %d is negative",
wraplength);
FAIL_ZERO_RETURN(
errctx,
TTF_GetStringSizeWrapped(font, text, 0, wraplength, w, h),
AKGL_ERR_SDL,
"%s",
SDL_GetError());
SUCCEED_RETURN(errctx);
}