69 lines
3.0 KiB
Plaintext
69 lines
3.0 KiB
Plaintext
;;;; raylib [text] example - text writing anim
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;;;;
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;;;; examples/text/text_writing_anim.c. Sixty lines of C whose whole substance
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;;;; is one call this package cannot bind:
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;;;;
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;;;; DrawText(TextSubtext(message, 0, framesCounter/10), ...)
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;;;;
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;;;; TextSubtext is in raylib.h and is not in the bindings, on the rule
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;;;; raylib.fln states for the whole Text* family: it answers a `char *` into
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;;;; a rotating static buffer, and declare-c refuses a returned pointer to
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;;;; memory the caller does not own. There is no missing line to add — the
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;;;; binding would be wrong at any signature.
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;;;;
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;;;; And it does not matter, because Flan has the operation as a primitive.
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;;;; `slice(a, lo, hi)` takes a view of an array, `string(b)` reinterprets the
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;;;; bytes as a string at no cost, and `string(slice(message, 0, n))` is
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;;;; TextSubtext with the static buffer removed — no copy, no shared state, no
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;;;; rotation to run out of. Porting the example is therefore how the gap gets
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;;;; *closed* rather than reported: the C's workaround for not having slices
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;;;; is the thing Flan did not need.
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;;;;
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;;;; The one place they differ, and it is why the clamp below is here rather
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;;;; than in the C: TextSubtext clips its length to the string, so the C can
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;;;; pass a counter that runs past the end for ever and see nothing happen.
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;;;; `slice` does not clip — an out-of-range bound is an error, and a bound
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;;;; computed at run time is checked at run time — so the length has to be
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;;;; brought inside the string before the call. That is a better failure than
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;;;; the C's, and it costs one `min`.
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;;;;
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;;;; The message is a `[u8]` and not a `string` because `slice` takes an array
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;;;; or a slice; `bytes-view("…")` is the bridge in the other direction from
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;;;; `string(…)` and costs nothing either. The embedded newline is written as
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;;;; an escape, and raylib's draw-text breaks the line on it.
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import rl "vendor:raylib"
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const screen-width = 800
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const screen-height = 450
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const message = "This sample illustrates a text writing\nanimation effect! Check it out! ;)"
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once frames-counter: i32
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fn main() -> ()
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rl/init-window(screen-width, screen-height,
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"raylib [text] example - text writing anim")
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defer rl/close-window()
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frames-counter = 0
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rl/set-target-fps(60)
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until rl/window-should-close()
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;; Update. Holding space runs the counter eight times faster; enter starts
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;; it over.
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if rl/is-key-down(:key-space)
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frames-counter += 8
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else
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frames-counter += 1
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if rl/is-key-pressed(:key-enter)
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frames-counter = 0
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;; Draw
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rl/with-drawing:
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rl/clear-background(rl/raywhite)
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;; One character every ten frames. The clamp is the whole difference from
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;; the C — see the header comment.
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let b = bytes-view(message)
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n = min(i32(length(b)), frames-counter / 10)
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rl/draw-text(str(slice(b, 0, n)), 210, 160, 20, rl/maroon)
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rl/draw-text("PRESS [ENTER] to RESTART!", 240, 260, 20, rl/lightgray)
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rl/draw-text("HOLD [SPACE] to SPEED UP!", 239, 300, 20, rl/lightgray)
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