First thing you'll need is 2 buffers, for the water. This needs to be an array of ints, same size as destination buffer. Arrange these in a 2-element array, to ease the flipping. Clear these to zero, and you're ready to start.
Calculating the new water is pretty simple. You'll need a loop that execute from 1 to height-1, then 1 to width - 1. At each element for the water, you'll need to sum the North, South, East, West points from the current water, and divide by 2 Not 4, 2. Then subtract the new water for [y][x] from this. This is your basic smooth function. Now you need to add the 'harmonic motion' to it. Take the new-water[y][x], shift it right x places (x could be 4) and subtract it from the new-water[y][x]. Pseudo-code for this might look like:
for y := 1 to height - 1
for x := 1 to width - 1
new-water[y][x] = ((old-water[y-1][x] +
old-water[y+1][x] +
old-water[y][x-1] +
old-water[y][x+1]) / 2) -
new-water[y][x])
new-water[y][x] -= new-water[y][x] shr x
end
end
Not too hard to make into working code. Because there are 2 pages, and we are
flipping between them, the references to what seem like uncalculated water
( - new-water[y][x]) are ok, because they come around and feed back. This is
all it takes to calculate the water! You may also want a part where you set
the 1 pixel wide frame around the water to 0, just to be safe.
Water is also pretty straightforward to paint. In fact some of the techniques here, you will see later on in the bump-mapping. Back to the task in hand. We will again need a loop for every pixel on the screen. What we need to do is calculate a kind-of normal at each pixel. This is simply:
offsetx = water[y][x] - water[y+1][x] offsety = water[y][x] - water[y][x+1]Which measures changes in X and Y. 'Colour' is then calculated by 128 - offsetx. Clip colour to the 0..255 range. Divide both offsetx and offsety by 8, and add them to x and y. Now for the tricky bit. You'll need a background image (or perhaps you can do without ...). You need to light the background image by the water. This is done by:
offsetx /= 3; offsety /= 8; indexu = offsetx + x; indexv = offsety + y; MulTable[backdrop[indexv*256+indexu]*256+colour];MulTable is another handy lookup table. It simply takes the value of (row*col) >> 8.
Pseudo code for this would be :
For y := 1 to height - 1
For x := 1 to width - 1
offsetx = water[y][x] - water[y+1][x]
offsety = water[y][x] - water[y][x+1]
colour = 128 - offsetx
trim colour to 0..255
divide offsetx and offsety by 8
add offsetx to x giving indexu
add offsety to y giving indexv
Plot (backdrop*colour) >> 8, lookup in table
End
End
What we are effectively doing here is applying fake lighting to the water, then mixing the colours. There are plenty of variations on calculating the normals. Plenty of room for exploration there.
Note it makes a difference what order you do calculations in. Its pretty simple though. You need to: