2021-04-09 18:33:39 (UTC-03:00)

Marcel Rodrigues <marcelgmr@gmail.com>

add BitMap

diff --git a/surf.lua b/surf.lua
new file mode 100644
index 0000000..b58ff23
--- /dev/null
+++ b/surf.lua
@@ -0,0 +1,109 @@
+local ffi = require "ffi"
+local bit = require "bit"
+
+ffi.cdef[[
+double hypot(double x, double y);
+double copysign(double x, double y);
+]]
+local mathx = ffi.C
+
+local bnot = bit.bnot
+local bor, band = bit.bor, bit.band
+local lshift, rshift =  bit.lshift,  bit.rshift
+
+local BitMap = {}
+BitMap.__index = BitMap
+
+local function new_bitmap(w, h)
+    local self = setmetatable({w=w, h=h}, BitMap)
+    self.t = math.ceil(w / 8) -- stride, i.e., bytes/row
+    self.p = ffi.new("unsigned char[?]", self.t * self.h)
+    return self
+end
+
+function BitMap:fill(v)
+    ffi.fill(self.p, self.t * self.h, v)
+end
+
+function BitMap:inside(x, y)
+    return x >= 0 and x < self.w and y >= 0 and y < self.h
+end
+
+function BitMap:_index_shift_mask(x, y)
+    assert(self:inside(x, y))
+    local index = y * self.t + math.floor(x / 8)
+    local shift = (7-x) % 8
+    local mask = lshift(1, shift)
+    return index, shift, mask
+end
+
+function BitMap:pget(x, y)
+    local index, shift, mask = self:_index_shift_mask(x, y)
+    return rshift(band(self.p[index], mask), shift)
+end
+
+function BitMap:pset(x, y, v)
+    local index, shift, mask = self:_index_shift_mask(x, y)
+    local byte = self.p[index]
+    if v > 0 then
+        byte = bor(byte, mask)
+    else
+        byte = band(byte, bnot(mask))
+    end
+    self.p[index] = byte
+end
+
+function BitMap:hline(x, y, w, v)
+    for i = x, x+w-1 do
+        self:pset(i, y, v)
+    end
+end
+
+function BitMap:vline(x, y, h, v)
+    for i = y, y+h-1 do
+        self:pset(x, i, v)
+    end
+end
+
+function BitMap:line(x0, y0, x1, y1, v)
+    if x1 == x0 then
+        if y1 > y0 then
+            self:vline(x0, y0, y1 - y0)
+        else
+            self:vline(x0, y1, y0 - y1)
+        end
+    elseif y1 == y0 then
+        if x1 > x0 then
+            self:hline(x0, y0, x1 - x0)
+        else
+            self:hline(x1, y0, x0 - x1)
+        end
+    else
+        local dx, dy = x1-x0, y1-y0
+        local sx, sy = mathx.copysign(1, dx), mathx.copysign(1, dy)
+        local de = math.abs(dy / dx)
+        local e = 0
+        local x, y = x0, y0
+        while x ~= x1 do
+            self:pset(x, y, v)
+            e = e + de
+            while e >= 0.5 do
+                self:pset(x, y, v)
+                y = y + sy
+                e = e - 1
+            end
+            x = x + sx
+        end
+    end
+end
+
+function BitMap:save_pbm(fname)
+    local pbm = io.open(fname, "wb")
+    pbm:write("P4\n", self.w, " ", self.h, "\n")
+    local row = self.p + 0
+    for y = 0, self.h-1 do
+        pbm:write(ffi.string(row, self.t))
+        row = row + self.t
+    end
+    pbm:close()
+end