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Updated "Size of a chunk" section of design docs

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Andrew Brown
2012-02-19 16:34:49 -05:00
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docs/design/designdoc.rst
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@@ -307,52 +307,40 @@ directions of the offsets are changed, but the amounts are the same.
The size of a chunk
-------------------
Now that we know how to place blocks relative to each other, we can begin to
construct a chunk section.
construct an entire chunk section.
Since the block sprites are 24 by 24 pixels, and the diagonal of the 16 by 16
grid is 16 squares, the width of one rendered chunk will be 384 pixels. Just
considering the top layer of the blocks:
grid is 16 squares, the width of one rendered chunk section will be 384 pixels.
Just considering the top layer of blocks within a section:
.. image:: cuberenderimgs/chunk_width.png
:alt: Illustrating the width of a single chunk
Since cubes next to each other in the same "diagonal row" are offset by 24
Since blocks next to each other in the same "diagonal row" are offset by 24
pixels, this is trivially calculated.
The height is a bit more tricky to calculate. Let's start by calculating the
height of a single stack of 128 cubes.
height of a single stack of 16 blocks.
If the top of a stack of cubes is at Y value 0, the 128th cube down must be
drawn (128-1)*12=1524 pixels below. However, that's not the end of the story.
The bottom cube has a height of 24 pixels, so the height of a rendered stack of
128 cube is 1548 pixels.
The non-overlapping edge of each block sprite is 12 pixels high. Since there are
16 blocks in this stack, that's 192 pixels high. There are also 6 additional
pixels at the top and bottom of the stack as shown, giving a total height of 204
pixels.
.. image:: cuberenderimgs/cube_stack128.png
:alt: A stack of 128 cubes takes 1560 vertical pixels to draw.
.. image:: cuberenderimgs/cube_stack16.png
:alt: A stack of 16 cubes takes 204 vertical pixels to draw.
You can also calculate this by looking at the sides of the cubes, which don't
overlap at all. They are 12 pixels each, times 128 cubes in the stack, gives
1536 pixels. Add in the 6 pixels for the top cube and the 6 pixels for the
bottom cube to get the total height of 1548 pixels.
So what about the entire chunk? Let's take a look at the top and bottom few
layers of a chunk.
But that's just for one column of blocks. What about the entire chunk section?
Take a look at this diagram:
.. image:: cuberenderimgs/chunk_height.png
:alt: The highest and lowest positioned cubes in a chunk
Let's let the red cubes represent the stack from above. The one on the top we'll
define as position 0, with our vertical axis running positively downward (as is
the case in a lot of imaging library coordinate systems) Therefore, the bottom
red cube is at vertical offset 1524 below.
The green highlighted blocks are the stack we calculated just above and have a
height of 204 pixels. The red highlighted blocks each take 12 pixels of vertical
space on the image, and there are 15 of them. So 204 + 12*15 is 384 pixels.
The green cube at the bottom most tip is the cube with the lowest vertical
placement on the image, so its offset plus 24 pixels for its height will be the
chunk height. Since the green cubes each have an offset of 12 pixels, add 15*12
pixels to get the offset of the lowest green cube: 1704.
So the total size of a chunk in pixels is 384 wide by 1728 tall. That's pretty
tall!
So the total size of a chunk section in pixels is 384 wide by 384 tall.
Assembling a Chunk
------------------