akbasic/tools/screenshot.c

/**
 * @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 not drawn unless a font is named.** A screenshot in the
 * graphics chapter is of the drawing, and a `READY` in the corner is noise in a
 * figure about `CIRCLE`; leaving the layer out also means no font has to be
 * found, which keeps this runnable from a build tree with no assets resolved.
 *
 * A figure of a program whose *output is text* needs the opposite, and
 * docs/17-tutorial-breakout.md is one: that game's wall, HUD and messages are
 * characters in the grid, so a picture without the text layer is a picture of
 * two sprites on a black field. Naming a font as the fifth argument swaps the
 * stdio sink for the akgl one and renders the grid before the sprites, in the
 * same order src/frontend_akgl.c uses. The fence attribute that asks for it is
 * `text=1`; tools/docs_screenshots.sh turns that into this argument.
 *
 * The sink is the akgl one *alone* rather than a tee, so a program's output
 * lands in the picture rather than on stdout -- which is what the caller reads
 * to decide a figure failed. Nothing is lost: `screenshot=` blocks are also run
 * by tests/docs_examples.sh, which is where a raised error is caught.
 */

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#include <SDL3/SDL.h>
#include <SDL3_image/SDL_image.h>
#include <SDL3_ttf/SDL_ttf.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/frontend.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;
/** @brief The text grid, and the font behind it. Only used when one is named. */
static akbasic_AkglSink GRIDSTATE;
static TTF_Font *FONT = NULL;
static akbasic_GraphicsBackend GRAPHICS;
static akbasic_AkglGraphics GRAPHICSSTATE;
static akbasic_SpriteBackend SPRITES;
static akbasic_AkglSprites SPRITESSTATE;
static akbasic_UiBackend UI;
static akbasic_AkglUi UISTATE;
/*
 * 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] [font.ttf] [grid]\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"
	    "\n"
	    "  Naming a font lends the program a UI device, because the widgets\n"
	    "  draw text and cannot come up without one. Passing 1 for `grid` as\n"
	    "  well draws the text layer, for a figure of a program whose output\n"
	    "  is characters rather than drawing.\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