mirror of
https://github.com/wisplite/cardstock-system.git
synced 2026-06-27 15:27:09 -05:00
wisplite
80 lines
2.3 KiB
Lua
80 lines
2.3 KiB
Lua
-- Convert a normal 24-bit RGB hex color (#RRGGBB or RRGGBB) to RGB565 (0..65535)
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local function hexConvert(hex)
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assert(type(hex) == "string", "hexConvert expects a string like '#RRGGBB'")
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hex = hex:gsub("^#", "")
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assert(#hex == 6, "hex color must be 6 hex digits (RRGGBB)")
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local r = tonumber(hex:sub(1, 2), 16)
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local g = tonumber(hex:sub(3, 4), 16)
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local b = tonumber(hex:sub(5, 6), 16)
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assert(r and g and b, "invalid hex color")
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-- RGB888 -> RGB565 (truncate, common in embedded code)
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local rgb565 = ((r & 0xF8) << 8) | ((g & 0xFC) << 3) | (b >> 3)
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return rgb565
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end
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local function clampInt(x, lo, hi)
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if x < lo then return lo end
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if x > hi then return hi end
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return x
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end
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-- Split RGB565 into channels:
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-- r: 0..31, g: 0..63, b: 0..31
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local function unpack565(c)
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c = c & 0xFFFF
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local r = (c >> 11) & 0x1F
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local g = (c >> 5) & 0x3F
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local b = c & 0x1F
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return r, g, b
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end
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local function pack565(r, g, b)
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r = r & 0x1F
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g = g & 0x3F
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b = b & 0x1F
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return (r << 11) | (g << 5) | b
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end
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-- Blend a foreground RGB565 color over a background RGB565 color, returning an RGB565 result.
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-- opacity:
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-- - 0..1 (float) OR 0..255 (int)
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-- - 0 means fully background, 1/255 means fully foreground
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local function withOpacity(fg565, bg565, opacity)
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assert(type(fg565) == "number" and type(bg565) == "number", "withOpacity expects (number fg565, number bg565, number opacity)")
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assert(type(opacity) == "number", "withOpacity opacity must be a number")
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local a
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if opacity <= 1 then
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a = math.floor(opacity * 255 + 0.5)
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else
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a = math.floor(opacity + 0.5)
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end
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a = clampInt(a, 0, 255)
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if a == 0 then return bg565 & 0xFFFF end
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if a == 255 then return fg565 & 0xFFFF end
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local fr, fg, fb = unpack565(fg565)
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local br, bg, bb = unpack565(bg565)
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-- out = bg + (fg - bg) * a
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-- done per-channel, with rounding.
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local r = math.floor((br * (255 - a) + fr * a + 127) / 255)
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local g = math.floor((bg * (255 - a) + fg * a + 127) / 255)
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local b = math.floor((bb * (255 - a) + fb * a + 127) / 255)
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return pack565(
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clampInt(r, 0, 31),
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clampInt(g, 0, 63),
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clampInt(b, 0, 31)
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)
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end
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return {
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hexConvert = hexConvert,
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withOpacity = withOpacity,
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} |