src/genlanczos.lua

   1 fnname = arg[1];
   2 src = tonumber(arg[2]);
   3 dest = tonumber(arg[3]);
   4 a = tonumber(arg[4]);
   5 bits8 = (arg[5] == "8");
   6
   7 coeffscale = 16384;
   8
   9 coeffs_for = function(xpos, srcsize, dstsize, alpha)
  10         local ret = {};
  11         local center = math.floor(xpos * srcsize / dstsize);
  12         for i = -alpha + 1, alpha do
  13                 local point = center + i;
  14                 local x = point + 0.5 - xpos * srcsize / dstsize - 0.5 * srcsize / dstsize;
  15                 if x < -1e-10 or x > 1e-10 then
  16                         local xpi = x * math.pi;
  17                         if point >= 0 and point < srcsize then
  18                                 ret[point] = a * math.sin(xpi) * math.sin(xpi / a) / (xpi * xpi);
  19                         end
  20                 else
  21                         if point >= 0 and point < srcsize then
  22                                 ret[point] = 1;
  23                         end
  24                 end
  25         end
  26         local sum = 0;
  27         local k, v;
  28         for k, v in pairs(ret) do
  29                 sum = sum + v;
  30         end
  31         for k, v in pairs(ret) do
  32                 ret[k] = math.floor(coeffscale * ret[k] / sum + 0.5);
  33         end
  34         return ret;
  35 end
  36
  37 emit_pixel = function(xpos, srcsize, dstsize, alpha)
  38         local t = coeffs_for(xpos, srcsize, dstsize, alpha);
  39         io.stdout:write("tmp[" .. xpos .. "]=(");
  40         for k,v in pairs(t) do
  41                 io.stdout:write(v .. "*src[" .. k .. "]+");
  42         end
  43         io.stdout:write("0)/" .. coeffscale .. ";\n");
  44 end
  45
  46 emit_fn_prologue = function(name, dstsize, b8f)
  47         if b8f then
  48                 io.stdout:write("void " .. name .. "(unsigned char* dst, unsigned char* src)\n");
  49         else
  50                 io.stdout:write("void " .. name .. "(unsigned short* dst, unsigned short* src)\n");
  51         end
  52         io.stdout:write("{\n");
  53         io.stdout:write("int tmp[" .. dstsize .. "];\n");
  54 end
  55
  56 emit_fn_epilogue = function(dstsize, b8f)
  57         io.stdout:write("for(int i = 0; i < " .. dstsize .. "; i++)\n");
  58         io.stdout:write("if(tmp[i] < 0) dst[i] = 0;\n");
  59         if b8f then
  60                 io.stdout:write("else if(tmp[i] > 255) dst[i] = 255;\n");
  61         else
  62                 io.stdout:write("else if(tmp[i] > 65535) dst[i] = 65535;\n");
  63         end
  64         io.stdout:write("else dst[i] = tmp[i];\n");
  65         io.stdout:write("}\n");
  66 end
  67
  68 emit_fn = function(name, srcsize, dstsize, alpha, b8f)
  69         emit_fn_prologue(name, dstsize, b8f);
  70         for i = 0, dstsize - 1 do
  71                 emit_pixel(i, srcsize, dstsize, alpha)
  72         end
  73         emit_fn_epilogue(dstsize, b8f);
  74 end
  75
  76 emit_fn(fnname, src, dest, a, bits8);