I need to draw a cylinder geometry using webgl, but don't know how to realize it. The parameters may be radius,subdivisions and two central point of bottom faces.Any ideas will be appreciated,thanks~
Fundamentally, you will build it with triangles. It would be easiest to think of it more as an "n-sided" prism. The top and bottom faces will need to be made of triangle "fans", where each triangle shares one point in the center.
You will need to use simple math (including trigonometry) to calculate the locations of the points for each triangle.
If you don't know how to draw triangles with WebGL, check out NeHe's excellent WebGL guide at learningwebgl.com.
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I created my own little 2D-Engine with DirectX (okey, should be more like a GUI in the end) and tried to create rounded edges for a simple Rectangle. Since I never done this with a graphics framework before I had no idea how to supply this.
For now, I just overlapped 5 Rectangles and 4 circles (the circles are used for the rounded edges). It does work with opaque colors but if I add alpha into the rectangles the circles are making problems. (Shown in the image below - i should have choose another colors...)
<# Open Image #>
I can't find a solution myself (I googled and whondered I found nothing about rounded edges in DirectX) and I do believe there is a much powerful and faster method doing this. So my final question is, what are the common algorythm to create a rectangle with rounded edges in Direct3D9 ?
The common way to draw rounded quads is the use of textures with an alphachannel. It's very easy and the most of the gui's uses images to achieve a specific look. If you draw only single-colored boxes it may look very generic after a while (even if they have fancy rounded corners ;) ).
But if you want to draw rounded quads directly, I would suppose to generate a custom geometry, which fits the desired area directly without overlapping (need for alphablending). In you case it would be something like this:
The more triangles you're using for the corner the smoother it will look.
I am trying to create an application similar in UI to Sketchup. As a first step, I need to display the ground surface stretching out in all directions. What is the best way to do this?
Options:
Create a sufficiently large regular polygon stretching out in all directions from the origin. Here there is a possibility of the user hitting the edges and falling off the surface of the earth.
Model the surface of the earth as a sphere/spheroid. Here I will be limiting my vertex co-ordinates to very large values prone to rounding off errors. (Radius of earth is 6371000000 millimeter).
Same as 1 but dynamically extend the ends of the earth as the user gets close to them.
What is the usual practice?
I guess you would do neither of these, but instead use a virtual ground.
So you just find out, what portion of the ground is visible in the viewport and then create a plane large enough to fill that. With some reasonable maxiumum, which simulates the end of the line of sight aka horizon as we know it.
I'm using DirectX10 to simulate a water surface, and I'm now with a height map,which is a 2D array of the heights(y) at the points (x,z). But to draw it on the screen, I must turn it into a mesh or have a index to draw triangle topology.
But the data is too large to do it manually. Are there any methods for me to draw it on the screen. I hope it's easy to implement. If there is function included in DirectX10 which can make it, the it's the best one for me.
Create a mesh that format a grid of squares (each made of two triangles) and set all vertices y = 0. In the vertex shader sample the heightmap and add the value stored in the heightmap to the y of the vertice.
This might help you.
P.S: If the area you want it to cover is too big you should take a look at terrain LOD techniques (should work the same for water).
I'm sure you can make a mesh out of it. I doubt you can generate the heightmap for a water surface that is too large to "meshify".
Why are you looking at Diamond square. For a 512x512 heightmap all you need to do is define a set of point and then generate the triangles for it. Its really very simple.
Huh, you can build a sphere from squares, triangles, hexagons and so on and so forth, but I was wondering... which option is the most viable one?
Well, once again that's a question that differs a lot by preference and so on, but I was thinking more of what is easier to process for a computer.
Like, there will be different amount of segments when the sphere is built from triangles, squares or hexagons.
The idea behind this is to get the shape, which uses the least segments to form a sphere.
Optional: which shape would provide the best connectivity? Like, with squares, you can form topmost points with triangles, all connecting to one point. But probably there are shapes that can provide seamless results, that all the sphere consists of only 1 shape.
Triangles are used for tessellation of this type. You can form anything from them without any gaps/overlap.
I need to create a (large) set of spatial polygons for test purposes. Is there an algorithm that will create a randomly shaped polygon staying within a bounding envelope? I'm using OGC Simple stuff so a routine to create the well known text is the most useful, Language of choice is C# but it's not that important.
Here you can find two examples of how to generate random convex polygons. They both are in Java, but should be easy to rewrite them to C#:
Generate Polygon example from Sun
from JTS mailing list, post Minimum Area bounding box by Michael Bedward
Another possible approach based on generating set of random points and employ Delaunay tessellation.
Generally, problem of generating proper random polygons is not trivial.
Do they really need to be random, or would some real WKT do? Because if it will, just go to http://koordinates.com/ and download a few layers.
What shape is your bounding envelope ? If it's a rectangle, then generate your random polygon as a list of points within [0,1]x[0,1] and scale to the size of your rectangle.
If the envelope is not a rectangle things get a little more tricky. In this case you might get best performance simply by generating points inside the unit square and rejecting any which lie in the part of the unit square which does not scale to the bounding envelope of your choice.
HTH
Mark
Supplement
If you wanted only convex polygons you'd use one of the convex hull algorithms. Since you don't seem to want only convex polygons your suggestion of a circular sweep would work.
But you might find it simpler to sweep along a line parallel to either the x- or y-axis. Assume the x-axis.
Sort the points into x-order.
Select the leftmost (ie first) point. At the y-coordinate of this point draw an imaginary horizontal line across the unit square. Prepare to create a list of points along the boundary of the polygon above the imaginary line, and another list along the boundary below it.
Select the next point. Add it to the upper or lower boundary list as determined by it's y-coordinate.
Continue until you're out of points.
This will generate convex and non-convex polygons, but the non-convexity will be of a fairly limited form. No inlets or twists and turns.
Another Thought
To avoid edge crossings and to avoid a circular sweep after generating your random points inside the unit square you could:
Generate random points inside the unit circle in polar coordinates, ie (r, theta).
Sort the points in theta order.
Transform to cartesian coordinates.
Scale the unit circle to a bounding ellipse of your choice.
Off the top of my head, that seems to work OK