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A few changes.

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git-svn-id: svn://svn.code.sf.net/p/sc2/code/trunk@2533 8092fc87-c524-0410-9efc-e669fe64eaf9
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meep-eep
2006-11-24 23:47:57 +00:00
parent 7ec4827822
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1 changed files with 23 additions and 21 deletions
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@@ -3,8 +3,7 @@ Planet Topography Code: sc2code/planets/gentopo.c
This text covers only topography generation code. It does NOT cover the This text covers only topography generation code. It does NOT cover the
craters (blemishes) nor the smoothing. Variables names are the same in craters (blemishes) nor the smoothing. Variables names are the same in
"sc2code/planets/gentopo.c", so keep this file open while reading this "sc2code/planets/gentopo.c".
doc.
A brief overview: A brief overview:
@@ -12,7 +11,7 @@ The algorithm works by applying several elevation/lowering steps on the
same terrain. Each step works by randomly generating two non-intersecting same terrain. Each step works by randomly generating two non-intersecting
lines, LineDDA0 and LineDDA1. That delimits two regions. Each region is lines, LineDDA0 and LineDDA1. That delimits two regions. Each region is
then displaced by a certain height delta (depth_delta). That step is then displaced by a certain height delta (depth_delta). That step is
repeated several times, until we have a decent topography. repeated several times.
There's a pseudocode below, with detailed information about it in the next There's a pseudocode below, with detailed information about it in the next
section. section.
@@ -21,28 +20,29 @@ The DeltaTopography() function works as follows:
Function parameters: Function parameters:
COUNT num_iterations ///> Number of height displacements on COUNT num_iterations // Number of height displacements on the
the planet's surface // planet's surface
PSBYTE DepthArray ///> Target surface, receives topography data PSBYTE DepthArray // Target surface, receives topography data
PRECT pRect ///> Surface dimensions PRECT pRect // Surface dimensions
SIZE depth_delta ///> The amount of height units to SIZE depth_delta // The amount of height units to raise/lower
increase/decrease on each displacement // on each displacement
for i from 1 to num_iterations for i from 1 to num_iterations
randomly either negates depth_delta's or not, which influences the displacement direction randomly either negates depth_delta's or not, influencing
randomly pick two line segments, LineDDA0 and LineDDA1 the displacement direction
increase the height of the region between LineDDA0 and randomly pick two line segments, LineDDA0 and LineDDA1
LineDDA1 by depth_delta increase the height of the region between LineDDA0 and
decrease the height of the region between LineDDA1 and LineDDA1 by depth_delta
LineDDA0 by depth_delta (by wrapping around the surface) decrease the height of the region between LineDDA1 and
LineDDA0 by depth_delta (by wrapping around the surface)
end for end for
Detailed information about the algorithm's steps: Detailed information about the algorithm's steps:
First, in half the steps (randomly) depth_delta is negated. First, in half the steps (randomly) depth_delta is negated.
That influences on the direction of the displacements. It is That influences on the direction of the displacements.
important to note that, in each step, exactly two height Note that in each step exactly two height displacements occur:
displacements occur: a lifting and a lowering. a lifting and a lowering.
Next, it sets both w1 and w2 to different random WORD values. Those are Next, it sets both w1 and w2 to different random WORD values. Those are
used in the line segment generation process. used in the line segment generation process.
@@ -50,7 +50,7 @@ used in the line segment generation process.
LineDDA0 starts on a random position on the top of the surface, and ends LineDDA0 starts on a random position on the top of the surface, and ends
at another random position on the bottom of the surface. at another random position on the bottom of the surface.
LineDDA0 never wraps around the surface, since their X coordinates are LineDDA0 never wraps around the surface, since their X coordinates are
generated in the range 0->width: generated in the range 0..width-1:
LineDDA0.x_top = LOBYTE (w1) % width; LineDDA0.x_top = LOBYTE (w1) % width;
LineDDA0.x_bot = HIBYTE (w1) % width; LineDDA0.x_bot = HIBYTE (w1) % width;
@@ -65,7 +65,7 @@ Y coordinates are 0 for top, and 'height' for bottom in both line
segments. segments.
This delimits basically two regions. One delimited by LineDDA0 on the left This delimits basically two regions. One delimited by LineDDA0 on the left
side, and LineDDA1 on the right right, which we call "0->1". Another one is side, and LineDDA1 on the right right, which we call "0->1". The other is
delimited by LineDDA1 on the left, and LineDDA0 on the right, which we call delimited by LineDDA1 on the left, and LineDDA0 on the right, which we call
"1->0". "1->0".
Note that, since we're talking about a planet, the rightmost side of the Note that, since we're talking about a planet, the rightmost side of the
@@ -77,7 +77,7 @@ The final step in the iteration is to increase the height of the region
delta_depth may be negative, raising part of the surface by delta_depth delta_depth may be negative, raising part of the surface by delta_depth
may result in the surface being lowered. may result in the surface being lowered.
By repeating this step num_iteration times we have a nice terrain generator. This step is repeated num_iteration times.
About the terrain generation algorithm: This method of displacing About the terrain generation algorithm: This method of displacing
line-delimited subsets of a surface is commonly known as Fault Formation. line-delimited subsets of a surface is commonly known as Fault Formation.
@@ -88,3 +88,5 @@ LineDDA0 and LineDDA1.
The first version of this document was written by: The first version of this document was written by:
Daniel Ribeiro Maciel <daniel.maciel@gmail.com> Daniel Ribeiro Maciel <daniel.maciel@gmail.com>
on 2006-11-24 on 2006-11-24