I need to measure the angle between a flat surface and a cylindrical surface with opencascade. For example for holes.
When i try to use Angle_dimension, all times return 0.
Maybe someone know how to do this.
Thank you in advance
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I have a 3D scene I'm drawing and I want to draw a rectangle for a dialogue text that will be stretched for all the screen's width, what's the best way to achieve this, having performance in mind?
I found about glOrtho() that I can use for exact pixel placing, but since it's a matrix multiplication task, won't my app feel much heavier during scenes with dialogues?
If yes, should I try to find a math solution to find the X position of my left window corner according to some Z distance and draw a QUAD from there? (Is this even possible?)
glOrtho() is the way to go.
In the course of OpenGL's rendering Pipeline, during the Primitive Assembly stage, every vertex will be transformed (projected) from eye coordinates to clip coordinates. Whether your projection matrix is used for 3D perspective or 2D orthogonalization, it's still one matrix multiplication per vertex before Rasterization starts.
glOrtho() will change your projection matrix to an orthographic one but the matrix only needs to be generated once per frame and the equations required to do so are very simple:
(image credit: MSDN)
Once you have a projection matrix, don't let the thought of matrix multiplication scare you. It's exactly what video cards are designed to do and it's hardly a frightening task for any processor or GPU these days.
I have a struct QUAD that stores 4 pointers to 4 VECTOR3D (which contains 3 floats) so that I can draw the quad mesh.
From what I understand is whenever I draw a mesh, I need normal as well to properly light/shade a mesh and it's relatively easy when it's a mesh laying on a plain, using normal per face.
When I have 2 by 2 quad meshes laying on XZ coordinate and tried to raise it's centre (0,0,0) by a certain point, say (0, 4, 0) it would start to form real 3D shapes, then I need to calculate normals again. I'm having hard time understanding how and what is to be to calculated normals. As expected, the 3D shape shades like it's still a flat mesh, so it does not represent real shape. One of the explanation says I need to calculate normals per vertex instead of per face.
Does it mean I need to calculate normals for all corners of mesh? once i have normals what would i do? I was still using old glBegin glEnd methods but now I feel like i need to use DrawArray method. I'm deeply confused and I'm pretty sure I don't make much sound but i'd much appreciate your help.
If you need flat looking surface then your normals will be normals to the quad plane. If you need "soft looking" surface you need to blend(read this and watch this cool simple video) normals - that will add sort of gradient.
Greetings all,
As seen in the image , I draw lots of contours using GL_LINE_STRIP.
But the contours look like a mess and I wondering how I can make this look good.(to see the depth..etc )
I must render contours so , i have to stick with GL_LINE_STRIP.I am wondering how I can enable lighting for this?
Thanks in advance
Original image
http://oi53.tinypic.com/287je40.jpg
Lighting contours isn't going to do much good, but you could use fog or manually set the line colors based on distance (or even altitude) to give a depth effect.
Updated:
umanga, at first I thought lighting wouldn't work because lighting is based on surface normal vectors - and you have no surfaces. However #roe pointed out that normal vectors are actually per vertex in OpenGL, and as such, any POLYLINE can have normals. So that would be an option.
It's not entirely clear what the normal should be for a 3D line, as #Julien said. The question is how to define normals for the contour lines such that the resulting lighting makes visual sense and helps clarify the depth?
If all the vertices in each contour are coplanar (e.g. in the XY plane), you could set the 3D normal to be the 2D normal, with 0 as the Z coordinate. The resulting lighting would give a visual sense of shape, though maybe not of depth.
If you know the slope of the surface (assuming there is a surface) at each point along the line, you could use the surface normal and do a better job of showing depth; this is essentially like a hill-shading applied only to the contour lines. The question then is why not display the whole surface?
End of update
+1 to Ben's suggestion of setting the line colors based on altitude (is it topographic contours?) or based on distance from viewer. You could also fill the polygon surrounded by each contour with a similar color, as in http://en.wikipedia.org/wiki/File:IsraelCVFRtopography.jpg
Another way to make the lines clearer would be to have fewer of them... can you adjust the density of the contours? E.g. one contour line per 5ft height difference instead of per 1ft, or whatever the units are. Depending on what it is you're drawing contours of.
Other techniques for elucidating depth include stereoscopy, and rotating the image in 3D while the viewer is watching.
If your looking for shading then you would normally convert the contours to a solid. The usual way to do that is to build a mesh by setting up 4 corner points at zero height at the bounds or beyond then dropping the contours into the mesh and getting the mesh to triangulate the coords in. Once done you then have a triangulated solid hull for which you can find the normals and smooth them over adjacent faces to create smooth terrain.
To triangulate the mesh one normally uses the Delaunay algorithm which is a bit of a beast but there does exist libraries for doing it. The best of which I know of is the ones based on Guibas as Stolfi papers since its pretty optimal.
To generate the normals you do a simple cross product and ensure the facing is correct and manually renormalize them before feeding into the glNormal.
The in the old days you used to make a glList out of the result but the newer way is to make a vertex array. If you want to be extra flash then you can look for coincident planar faces and optimize the mesh down for faster redraw but thats a bit of a black art - good for games, not so good for CAD.
(thx for bonus last time)
I'm using OpenGL and was told I should draw circles at each vertex of my outline to get smoothness. I tried this and it works great. The problem is speed. It crippled my application to draw a circle at each vertex. I'm not sure how else to fix the anomaly of my outlines other than circles, but using display lists and trying with vertex array both were brutally slow. Thanks
see: Edges on polygon outlines not always correct
One (perhaps too fancy) alternative is to draw a single polygon that bounds the circle (say, a quad), and then use a fragment program to discard the fragments. This would not be entirely trivial to write, but I would bet it's the fastest way.
You would simply pass the circle parameters to the fragment program and discard the fragment if the distance from the fragment center to the center of the circle is bigger than the desired radius.
Have you seen this article?
..or if you have access to the GL utility library, you could use gluDisk
I need to draw a circle on some arbitrary non plane surface, but this circle should lay on surface and follow surface's irregular form. In other words ( that is actuially can be one of possible solutions) want to have a "shadow" like projection on non plane surface near the mouse pointer. Do I need to create in memory a sphere and project it on the surface ? Are there some other techniques to achieve the same goal?
Thank you in advance.
There are two ways to do this. First would be, to create a cylinder and intersect it with the surface, get the intersection segments, and draw them. If you already have a math library which you can leverage, and if you don't have to do intersections every frame, then this might be a good idea. You will get accurately what you want.
The other option, as you already suggested would be to use a projection. I am not sure though that, you will be able to see clearly the shadow of a circle on a surface. If however, you have parametric texture coordinates for your surface, you can create a texture with the circle imprinted on it, and apply this texture to the surface.