initial commit

syslib/gfxplus.lua

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