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Generate the documentation's figures from the listings they illustrate

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Chapters 6 and 8 described what a verb draws in prose. Eight figures now show
it, and each one is produced by running the BASIC listing printed immediately
above it -- so a picture cannot drift away from the code beside it, which is the
way a screenshot goes wrong and the way nothing notices.

tools/screenshot.c is a second SDL host, much smaller than the frontend: dummy
video driver, software renderer, run to completion, read the target back, write
a PNG. It draws no text layer on purpose, so a READY in the corner is not noise
in a figure about BOX and no font has to be resolved.

tools/docs_screenshots.sh reads the new screenshot=NAME fence tag straight out
of the markdown. size=WxH is the second tag, and SCALE's figure uses it: the
point being made is a 320x200 listing filling a larger window, which cannot be
made on a 320x200 surface.

Two gates, answering different questions. docs_examples fails a tagged block
with no image, in both configurations, so a figure cannot be added and
forgotten. docs_screenshots -- a CTest, AKGL build only -- re-renders every
figure and compares byte for byte, so a listing edited without regenerating
fails. Only the second catches a stale picture.

The PNGs are checked in because a reader on the forge has no build tree, and
docs/images/README.md says loudly that they are generated. Regenerating is never
part of a build: the target is run deliberately, so a make cannot put eight
binary diffs in front of whoever ran it.

Drawing the BOX figure caught a defect in TODO.md itself. Deviation 16 claimed
in bold that BOX fills on a negative angle while its own paragraph said the fill
was filed rather than implemented. BOX cannot fill, and filled_rect is reached
by no verb as a result.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
This commit is contained in:
Andrew Kesterson
2026-08-01 07:37:04 -04:00
parent 737fdc760f
commit 16b38c1138
18 changed files with 759 additions and 40 deletions
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217
tools/screenshot.c Normal file
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/**
* @file screenshot.c
* @brief Run one BASIC program against an offscreen renderer and save a PNG.
*
* The documentation's graphics and sprite chapters describe what a verb draws,
* and a sentence is a poor way to describe a picture. This is what turns the
* listing in a chapter into the image beside it -- tools/docs_screenshots.sh
* extracts the listing from the markdown and hands it here, so the picture is
* generated from the exact program the reader is looking at rather than from a
* copy that can drift away from it.
*
* **It is a host, like src/frontend_akgl.c**, and it is deliberately a separate
* one: the frontend opens a real window, pumps events and never stops until the
* script quits, none of which a build step wants. What this does instead is the
* shortest path to pixels -- the dummy video driver, a software renderer, run to
* completion, read the target back, write it out. deps/libakgl/tests/draw.c and
* tests/akgl_backends.c set that pattern; this is the third user of it.
*
* **The text layer is deliberately not drawn.** A screenshot in the graphics
* chapter is of the drawing, and a `READY` in the corner is noise in a figure
* about `CIRCLE`. It also means no font has to be found, which keeps this
* runnable from a build tree with no assets resolved.
*/
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <SDL3/SDL.h>
#include <SDL3_image/SDL_image.h>
#include <akerror.h>
#include <akgl/error.h>
/*
* game.h for the `renderer` and `camera` globals: akgl_actor_render() reads
* both without taking either as an argument, so a host that never calls
* akgl_game_init() -- which is every host here, because owning the game loop is
* what goal 3 forbids -- populates them itself. Same three lines as
* src/frontend_akgl.c and tests/akgl_backends.c, and each says so.
*/
#include <akgl/game.h>
#include <akgl/heap.h>
#include <akgl/registry.h>
#include <akgl/renderer.h>
#include <akbasic/akgl.h>
#include <akbasic/error.h>
#include <akbasic/runtime.h>
#include <akbasic/sink.h>
/** @brief The interpreter carries every pool it owns, so it does not fit on a stack. */
static akbasic_Runtime RUNTIME;
static akbasic_TextSink SINK;
static akbasic_StdioSink SINKSTATE;
static akbasic_GraphicsBackend GRAPHICS;
static akbasic_AkglGraphics GRAPHICSSTATE;
static akbasic_SpriteBackend SPRITES;
static akbasic_AkglSprites SPRITESSTATE;
/*
* No `window` of our own: akgl/game.h declares one as an unprefixed extern --
* libakgl's TODO calls that a defect and it is -- so a static here shadows it
* and the file will not compile. Writing the global is what a host does anyway.
*/
/** @brief The whole program, read in one go. Longer than any figure's listing. */
static char SOURCE[65536];
static void usage(void)
{
fprintf(stderr,
"usage: akbasic_screenshot <program.bas> <output.png> [width] [height]\n"
"\n"
" Runs the program against an offscreen renderer of the given size\n"
" (default 320x200) and writes what it drew as a PNG.\n");
}
/** @brief Slurp the program. A figure's listing is small; a partial read is not tolerated. */
static akerr_ErrorContext AKERR_NOIGNORE *read_program(const char *path)
{
PREPARE_ERROR(errctx);
FILE *in = NULL;
size_t got = 0;
memset(SOURCE, 0, sizeof(SOURCE));
in = fopen(path, "r");
FAIL_ZERO_RETURN(errctx, (in != NULL), AKERR_IO, "could not open %s", path);
got = fread(SOURCE, 1, sizeof(SOURCE) - 1, in);
fclose(in);
FAIL_ZERO_RETURN(errctx, (got > 0), AKERR_IO, "%s is empty", path);
FAIL_ZERO_RETURN(errctx, (got < sizeof(SOURCE) - 1), AKERR_OUTOFBOUNDS,
"%s is longer than %zu bytes", path, sizeof(SOURCE) - 1);
SUCCEED_RETURN(errctx);
}
/**
* @brief Everything between SDL being up and the pixels being readable.
*
* Split out so the ATTEMPT in main() has one thing to CATCH and the SDL
* teardown has one place to happen.
*/
static akerr_ErrorContext AKERR_NOIGNORE *draw_program(const char *outpath, int w, int h)
{
PREPARE_ERROR(errctx);
SDL_Surface *shot = NULL;
PASS(errctx, akgl_error_init());
renderer = &_akgl_renderer;
FAIL_ZERO_RETURN(errctx, SDL_Init(SDL_INIT_VIDEO), AKGL_ERR_SDL,
"Couldn't initialize SDL: %s", SDL_GetError());
FAIL_ZERO_RETURN(errctx,
SDL_CreateWindowAndRenderer("net/aklabs/akbasic/screenshot", w, h, 0,
&window, &renderer->sdl_renderer),
AKGL_ERR_SDL, "Couldn't create window/renderer: %s", SDL_GetError());
PASS(errctx, akgl_render_bind2d(renderer));
PASS(errctx, akgl_heap_init());
PASS(errctx, akgl_registry_init());
camera = &_akgl_camera;
camera->x = 0.0f;
camera->y = 0.0f;
camera->w = (float32_t)w;
camera->h = (float32_t)h;
/*
* Opaque black, so a figure has a defined background rather than whatever
* the driver left in the buffer. GRAPHIC's own clear is a filled rectangle
* over the output for a reason src/graphics_akgl.c explains -- clearing is
* the host's prerogative -- and this is the host doing it.
*/
FAIL_ZERO_RETURN(errctx, SDL_SetRenderDrawColor(renderer->sdl_renderer, 0, 0, 0, 0xff),
AKGL_ERR_SDL, "%s", SDL_GetError());
FAIL_ZERO_RETURN(errctx, SDL_RenderClear(renderer->sdl_renderer),
AKGL_ERR_SDL, "%s", SDL_GetError());
/* stdout: a program that errors puts its "? line : CLASS message" there,
which is what the caller shows when a figure comes out wrong. */
PASS(errctx, akbasic_sink_init_stdio(&SINK, &SINKSTATE, stdout, NULL));
PASS(errctx, akbasic_runtime_init(&RUNTIME, &SINK));
PASS(errctx, akbasic_graphics_init_akgl(&GRAPHICS, &GRAPHICSSTATE, renderer));
PASS(errctx, akbasic_sprite_init_akgl(&SPRITES, &SPRITESSTATE, renderer, &GRAPHICSSTATE));
PASS(errctx, akbasic_runtime_set_devices(&RUNTIME, &GRAPHICS, NULL, NULL, &SPRITES));
PASS(errctx, akbasic_runtime_load(&RUNTIME, SOURCE));
PASS(errctx, akbasic_runtime_start(&RUNTIME, AKBASIC_MODE_RUN));
PASS(errctx, akbasic_runtime_run(&RUNTIME, 0));
/*
* The drawing verbs are immediate and are already on the target. Sprites are
* not: they are libakgl actors and reach the target through a render pass,
* which in the standalone frontend is part of a frame. There is no frame
* here, so this is it.
*/
PASS(errctx, akbasic_sprite_akgl_render(&SPRITES));
shot = SDL_RenderReadPixels(renderer->sdl_renderer, NULL);
FAIL_ZERO_RETURN(errctx, (shot != NULL), AKGL_ERR_SDL,
"Couldn't read the target back: %s", SDL_GetError());
if ( !IMG_SavePNG(shot, outpath) ) {
SDL_DestroySurface(shot);
FAIL_RETURN(errctx, AKGL_ERR_SDL, "Couldn't write %s: %s", outpath, SDL_GetError());
}
SDL_DestroySurface(shot);
SUCCEED_RETURN(errctx);
}
int main(int argc, char **argv)
{
PREPARE_ERROR(errctx);
int w = 320;
int h = 200;
if ( argc < 3 ) {
usage();
return 2;
}
if ( argc > 3 ) {
w = atoi(argv[3]);
}
if ( argc > 4 ) {
h = atoi(argv[4]);
}
if ( w <= 0 || h <= 0 ) {
usage();
return 2;
}
/*
* Set here rather than left to the environment so the tool answers the same
* on a developer's desktop as it does in CI. A figure regenerated over a
* real GPU could differ by a pixel of antialiasing and turn every rebuild
* into a diff.
*/
SDL_SetHint(SDL_HINT_VIDEO_DRIVER, "dummy");
SDL_SetHint(SDL_HINT_RENDER_DRIVER, "software");
ATTEMPT {
CATCH(errctx, read_program(argv[1]));
CATCH(errctx, draw_program(argv[2], w, h));
} CLEANUP {
if ( window != NULL ) {
SDL_DestroyWindow(window);
window = NULL;
}
SDL_Quit();
} PROCESS(errctx) {
} HANDLE_DEFAULT(errctx) {
LOG_ERROR_WITH_MESSAGE(errctx, "could not draw the screenshot");
return 1;
/*
* FINISH_NORETURN rather than FINISH, matching src/main.c and
* tests/akgl_backends.c: FINISH expands a `return __err_context` that
* this int-returning function cannot compile even where the branch is
* unreachable.
*/
} FINISH_NORETURN(errctx);
return 0;
}