I am in front a simple issue, but I can't find a way to solve it:
I have the coordinates of a lightning source. I would like to draw a white circle centered on this lightning source.
How can I do that? Is there a opengl function or I should add manually verteces to create a circle?
Thanks
OpenGL does not have primitives like circles. It only has triangles, fundamentally.
Your best options are either to make a regular n-gon where n is large enough to satisfy you, or make the circle geometry part of a texture, and just render a square where some of the coordinates are transparent.
Which is most appropriate depends entirely on context.
Use Blender to create a simple circle mesh. Export to one of the available object files, load it in your app and render. You can use Assimp to load the mesh or write your own loader. You can find a lot of examples online on how to do this.
Related
I have model of skull loaded from .obj file based on this tutorial . As long as I understand texture mapping of cube (make triangle on texture in range of [0,1], select one of six side, select triangle of two triangles on this side and map it with your triangle from texture), I have problem with thinking for any solution to texture mapping my skull. There are few thousands of triangles on it and I think that texture mapping them manually is more than wrong.
Is there any solution for this problem? I'll appreciate any piece of code since it may tell me more than just description of solution.
You can generate your UV coordinates automatically, but this will probably produce badly looking ouput except for very simple textures.
For detailed textures that have eyes, ears, etc., you need to crate your UV coordinates by hand in some 3d modeling tool like is Blender 3d, 3DS Max etc... There is a lot of tutorials all over the internet how to do that. (https://www.youtube.com/watch?v=eCGGe4jLo3M)
I have been asked to do 3D sphere and adding textures to it so that it looks like different planets in the Solar System. However 3ds max was not mentioned as mandatory.
So, how can I make 3D spheres using OpenGL and add textures to it? using glutsphere or am I suppose to do it some other method and how to textures ?
The obvious route would be gluSphere (note, it's glu, not glut) with gluQuadricTexture to get the texturing done.
I am not sure if glutSolidSphere has texture coordinates (as far as I can remeber they were not correct, or not existant). I remember that this was a great resource to get me started on the subject though:
http://paulbourke.net/texture_colour/texturemap/
EDIT:
I just remembered that subdividing an icosahedron gives a better sphere. Also texture coordinates are easier to implement that way:
see here:
http://www.gamedev.net/topic/116312-request-for-help-texture-mapping-a-subdivided-icosahedron/
and
http://www.sulaco.co.za/drawing_icosahedron_tutorial.htm
and
http://student.ulb.ac.be/~claugero/sphere/
I would like to draw a simple 2D stickman on the screen. I also want it to be anti-aliased.
The problem is that I want to use a bones system, which will be written after I would know how to draw the stickman itself based on the joints positions. This means I can't use sprites - I want my stickman to be fully controlable in the code.
It would be great if it will be possible to draw curves too.
Drawing a 3D stickman using a model would also be great if not better. The camera will be positioned like it's 2D, but I would still have depth. The problem is that I only have experience in Maya, and exporting and vertex weighting of the model in OpenGL seems like a mess...
I tried to find libraries for 2D anti-aliased drawing or enable multi-sampling and draw normally, but I had no luck. I also tried to use OpenGL's native anti-aliasing but it seems deprecated and the line joins are bad...
I don't want it to be too complicated because, well, it shouldn't be - it's just the first part of my program, and it's drawing a stickman...
I hope you guys can help me, I'm sure you know better than me :)
You could enable GL_SMOOTH. To check if you device supports your required line width for smooth lines, you can use glGet(GL_SMOOTH_LINE_WIDTH_RANGE);
If you want your code to be generic, you can also use antialiased textures.
Take a look at this link
http://www.opengl.org/resources/code/samples/advanced/advanced97/notes/node62.html
The only way to get antialiasing is use GL library which knows how to get antialiased GL context, for example, SDL. As of stickman, you can draw him with colored polygons.
In OpenGL, how can one cut a triangle shaped hole from a square? making the hole transparent.
I'm also using SDL, maybe it can be achieved with an SDL surface?
While doing it on a texture is truly the easier way out, if you need it to be a real shape, you might try using the GLUtesselator from GLU toolkit. See a tutorial for it here.
General usage is that you create a tesselator object, create two contours (the outer and the inner in a reverse direction) and the tesselator translates that into pure OpenGL commands. Of course if it's efficiency you're seeking you should implement or find some higher order system that operates on vertex buffers.
You can use a texture and alpha blending: the texture would contain a transparent triangle. See this tutorial on blending.
EDIT: Of course alpha blending doesn't change the geometry. For that you need to perform treatments that are more complicated. See this tutorial on realtime CSG.
Reference: Constructive Solid Geometry
I have enjoyed learning to use OpenGL under the context of games programming, and I have experimented with creating small shapes. I'm wondering if there are any resources or apps that will generate code similar to the following with a simple paint-like interface.
glColor3f(1.0, 0.0, 0.0);
glBegin(GL_LINE_STRIP);
glVertex2f(1, 0);
glVertex2f(2, 3);
glVertex2f(4, 5);
glEnd();
I'm having trouble thinking of the correct dimensions to generate shapes and coming up with the correct co-ordinates.
To clarify, I'm not looking for a program I can just freely draw stuff in and expect it to create good code to use. Just more of a visual way of representing and modifying the sets of coordinates that you need.
I solved this to a degree by drawing a shape in paint and measuring the distances between the pixels relative to a single point, but it's not that elegant.
It sounds like you are looking for a way to import 2d geometry into your application. The best approach in my opinion would be to develop a content pipeline. It goes something like this:
You would create your content in a 3d modeling program like Google's Sketchup. In your case you would draw 2d shapes using polygons.
You need a conversion tool to get the data out of the original format and into a format that your target application can understand. One way to get polygon and vertex data out of Sketchup is to export to Collada and have your tool read and process it. (The simplest format would be a list of triangles or lines.)
Write a geometry loader in your code that reads the data created by your conversion tool. You need to write opengl code that uses vertex arrays to display the geometry.
The coordinates you'll use just depend on how you define your viewport and the resolution you're operating in. In fact, you might think about collecting the coordinates of the mouse clicks in whatever arbitrary coordinate system you want and then mapping those coordinates to opengl coordinates.
What kind of library are you expecting?
something like
drawSquare(dx,dy);?
drawCircle(radius);?
drawPoly(x1,y1,x2,y2....);?
Isn't that exactly the same as glVertex but with a different name? Where is the abstraction?
I made one of these... it would take a bitmap image, and generate geometry from it. try looking up triangulation.
the first step is generating the edge of the shape, converting it from pixels to vertices and edges, find all the edge pixels and put a vertex at each one, then based on either the distance between vertices, or (better) the difference in gradient between edges to cull out vertices and reduce the poly count of the mesh.
if your shape drawing program works with 'vector graphics' rather than pixels, i.e. plotting points and having lines drawn between them, then you can skip that first step and you just need to do triangulation.
the second step, once you have your edges and vertices is triangulation, in order to generate triangles, ear clipping is a simple method for instance.
as for the coordinates to use? that’s entirely up to you as others have said, to keep it simple, Id just work in pixel coordinates.
you can then scale and translate as needed to transform the shape for use.