init

.luacheckrc

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+globals = {
+	"isogen"
+}
+
+read_globals = {
+	-- Stdlib
+	string = {fields = {"split", "trim"}},
+	table = {fields = {"copy", "getn"}},
+
+	-- Minetest
+	"minetest", "vector", "ItemStack",
+	"dump", "dump2",
+	"VoxelArea",
+
+	-- deps
+	"mtt"
+}

draw.lua

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+-- x and y are 0-based
+local function get_index(w, x, y)
+    return (w * y) + x + 1
+end
+
+function isogen.draw_cube(data, width, cube_len, x_offset, y_offset, color1, color2, color3)
+    assert(cube_len % 4 == 0, "cube_len must be divisible by 4")
+    assert(cube_len > 4, "cube_len must be greater than 4")
+
+    local half_len_zero_indexed = (cube_len/2)-1
+    local quarter_len = cube_len / 4
+
+    -- left/right part
+    local yo = 0
+    for x=0,half_len_zero_indexed do
+        for y=0,half_len_zero_indexed do
+            -- left
+            local index = get_index(width, x_offset+x, y_offset+y+quarter_len+yo)
+            data[index] = color1
+            -- right
+            index = get_index(width, x_offset+cube_len-1-x, y_offset+y+quarter_len+yo)
+            data[index] = color2
+        end
+        if x % 2 == 0 then
+            yo = yo + 1
+        end
+    end
+
+    -- upper part
+    yo = 0
+    local yl = 1
+    for x=0,half_len_zero_indexed-1 do
+        for y=0,yl do
+            -- left
+            local index = get_index(width, x_offset+1+x, y_offset+quarter_len-1-yo+y)
+            data[index] = color3
+            -- right
+            index = get_index(width, x_offset+cube_len-2-x, y_offset+quarter_len-1-yo+y)
+            data[index] = color3
+        end
+        if x % 2 ~= 0 then
+            yo = yo + 1
+            yl = yl + 2
+        end
+    end
+end
+
+-- image width: (x * cube_len / 2) + (z * cube_len / 2)
+-- image height: (y * cube_len) - (cube_len / 2) -- XXX

draw.spec.lua

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+
+mtt.register("draw cube", function(callback)
+
+    local red = { a=255, r=255, g=0, b=0 }
+    local green = { a=255, r=0, g=255, b=0 }
+    local blue = { a=255, r=0, g=0, b=255 }
+    local transparent = { a=0, r=0, g=0, b=0 }
+
+    local width = 800
+    local height = 600
+    local png_data = {}
+
+    for i=1,width*height do
+        png_data[i] = transparent
+    end
+
+    isogen.draw_cube(png_data, width, 96, 0, 0, red, green, blue)
+    local png = minetest.encode_png(width, height, png_data)
+
+    local path = minetest.get_worldpath() .. "/test.png"
+    minetest.safe_file_write(path, png)
+
+    print("png saved: " .. #png .. " bytes")
+
+    callback()
+end)

init.lua

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+isogen = {}
+
+local MP = minetest.get_modpath("isogen")
+dofile(MP.."/draw.lua")
+
+if minetest.get_modpath("mtt") and mtt.enabled then
+    dofile(MP.."/draw.spec.lua")
+end

mod.conf

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+name = isogen