I want to make a 2D game in C++ using the Irrlicht engine. In this game, you will control a tiny ship in a cave of some sort. This cave will be created automatically (the game will have random levels) and will look like this:
Suppose I already have the the points of the polygon of the inside of the cave (the white part). How should I render this shape on the screen and use it for collision detection? From what I've read around different sites, I should use a triangulation algorithm to make meshes of the walls of the cave (the black part) using the polygon of the inside of the cave (the white part). Then, I can also use these meshes for collision detection. Is this really the best way to do it? Do you know if Irrlicht has some built-in functions that can help me achieve this?
Any advice will be apreciated.
Describing how to get an arbitrary polygonal shape to render using a given 3D engine is quite a lengthy process. Suffice to say that pretty much all 3D rendering is done in terms of triangles, and if you didn't use a tool to generate a model that is already composed of triangles, you'll need to generate triangles from whatever data you have there. Triangulating either the black space or the white space is probably the best way to do it, yes. Then you can build up a mesh or vertex list from that, and render those triangles that way. The triangles in the list then also double up for collision detection purposes.
I doubt Irrlicht has anything for triangulation as it's quite specific to your game design and not a general approach most people would take. (Typically they would have a tool which permits generation of the game geometry and the navigation geometry side by side.) It looks like it might be quite tricky given the shapes you have there.
One option is to use the map (image mask) directly to test for collision.
For example,
if map_points[sprite.x sprite.y] is black then
collision detected
assuming that your objects are images and they aren't real polygons.
In case you use real polygons you can have a "points sample" for every object shape,
and check the sample for collisions.
To check whether a point is inside or outside your polygon, you can simply count crossings. You know (0,0) is outside your polygon. Now draw a line from there to your test point (X,Y). If this line crosses an odd number of polygon edges (e.g. 1), it's inside the polygon . If the line crosses an even number of edges (e.g. 0 or 2), the point (X,Y) is outside the polygon. It's useful to run this algorithm on paper once to convince yourself.
Related
I'm still trying to density control (grade) meshes in CGAL. Specifically tet-meshing a polygon surface (or multiple surface manifolds) that I simply load as OFF files. I can also load lists of selected faces or face nodes too.
But I can't seem to get to first base on this with the polygon tet-mesher. All I want to do is assign and enforce a mesh density/size at selected faces in the OFF file.
I CAN get some kinds of mesh density working by inserting 1-D features with volumetric data meshing, but for CAD and 3D printing purposes it has to be computed from an STL-like triangular surface manifold, so volume-based meshing is not do-able.
Is what I'm trying to do even possible in CGAL? It feels to me like it must be, and I'm just missing something obvious.
I really hope someone can help here. FYI i'm mostly working with the Mesh3 example using v4.14.
Thanks very much.
Look at the Mesh_facet_criteria and in particular this constructor where SizingField is where you can control the size. For locating the point wrt a face, you can use the AABB-tree function closest_point_and_primitive().
I have a QuadTree which can be subdivided by placing objects in the nodes. I also have a planet made in OpenGL in the form of a Quad Sphere. The problem is i don't know how to put them together. How does a QuadTree store information about the Planet? Do i store vertices in the leaf Quad Tree nodes? And if so how do i split the vertex data into 4 sets without ruining the texturing and normals. If this is the case do i use Indices instead?
So my question in short really is:
How do i store my vertices data in a quad tree so that i can split the terrain on the planet up so that the planet will become higher detail at closer range. I assume this is done by using a Camera as the object that splits the nodes.
I've read many articles and most of them fail to cover this. The Quadtree is one of the most important things for my application as it will allow me to render many planets at the same time while still being able to get good definition at land. A pretty picture of my planet and it's HD sun:
A video of the planet can also be found Here.
I've managed to implement a simple quad tree on a flat plane but i keep getting massive holes as i think i'm getting the positions wrong. It's the last post on here - http://www.gamedev.net/topic/637956-opengl-procedural-planet-generation-quadtrees-and-geomipmapping/ and you can get the src there too. Any ideas how to fix it?
What you're looking for is an algorithm like ROAM (Real-time Optimally Adapting Mesh) to be able to increase or decrease the accuracy of your model based on the distance of the camera. The algorithm will make use of your quadtree then.
Check out this series on gamasutra on how to render a Real-time Procedural Universe.
Edit: the reason why you would use a quadtree with these methods is to minimize the number of vertices in areas where detail is not needed (flat terrain for example). The quadtree definition on wikipedia is pretty good, you should use that as a starting point. The goal is to create child nodes to your quadtree where you have changes in your "height" (you could generate the sides of your cube using an heightmap) until you reach a predefined depth. Maybe, as a first pass, you should try avoiding the quadtree and use a simple grid. When you get that working, you "optimize" your process by adding the quadtree.
To understand how quadtree and terrain data works together to achieve LOD based rendering
Read this paper. Easy to understand with illustrative examples.
I did once implement a LOD on a sphere. The idea is to start with a simple Dipyramid, the upper pyramid representing the northern sphere and the lower one representing the southern sphere. The the bases of the pyramids align with equator, the tips are on poles.
Then you subdivide each triangle into 4 smaller ones as much as you want by connecting the midpoints of the edges of the triangle.
The as much as you want is based on your needs, distance to camera and object placements could be your triggers for subdivision
I have a sprite with a triangle shape and I want to know when this triangle intersects with another object (a CCSPrite). I have been using CGRectIntersectsRect but it is not accurate because it take the bounding box of the the two sprites and not the actual shape.
--Edit
I think one way is to define several points around the actual triangle and check intersection between those points with another sprite. I am just wondering if there is an easier way to do this.
You can use box2d to detect collisions accurately. It can be useful if you have many different complicated shapes. Or you can just check intersections of shape's edges.
If there is many objects to detect collisions with, I offer to use box2d. It has good internal optimizations to be able to work with large amount of objects. In this case you will just have to create physical body equal to the your sprite's shape before adding object to your game layer.
I want to create a 2D game with monsters build as a custom vertex mesh and a texture map. I want to use this mesh to provide smooth vector animations. I'm using opengl es 2.0.
For now the best idea i have is to write a simple editor, where i can create a mesh and make key-frame based animation by changing position of each vertex and specifying the key-frames interpolation technics ( linear, quadric and so on).
I also have some understanding of bone animation (and skin based on bones), but i'm not sure i will be able to provide a good skeletons for my monsters.
I'm not sure it is a good way to go. Can you suggest some better ideas and / or editors, libraries for such mesh animations ?
PS: i'm using C++ now and so c++ libraries are the most welcome
You said this is a 2D game, so I'm going to assume your characters are flat polygons on to which you apply a texture map. Please add more detail to your question if this is not the case.
As far as the C++ part I think the same principles used for 3D blend shape animation can be applied to this case. For each character you will have a list of possible 'morph targets' or poses, each being a different polygon shape with same number of vertices. The character's AI will determine when to change from one to another, and how long a transition takes. So at any given point time your character can be either at a fixed state, matching one of your morph targets, or it can be in a transition state between two poses. The first has no trouble, the second case is handled by interpolating the vertices of the two polygons one by one to arrive to a morphed polygon. You can start with linear interpolation and see if that is sufficient, I suspect you may want to at least apply an easing function to the start and end of the transitions, maybe the smoothstep function.
As far as authoring these characters, have you considered using Blender? You can design and test your characters entirely within this package, then export the meshes as .obj files that you can easily import into your game.
I'm developing a game that basically has its entire terrain made out of AABB boxes. I know the verticies, minimum, and maximum of each box. I also set up my camera like this:
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
glRotatef(Camera.rotx,1,0,0);
glRotatef(Camera.roty,0,1,0);
glRotatef(Camera.rotz,0,0,1);
glTranslatef(-Camera.x,-Camera.y,-Camera.z);
What I'm trying to do is basically find the cube the mouse is on. I thought about giving the mouse position a forward directional vector and simply iterating through until the 'mouse bullet' hits something. However this envolves interating through all objects several times. Is there a way I could do it by only iterating through all the objects once?
Thanks
This is usually referred to as 'picking' This here looks like a good gl based link
If that is tldr, then a basic algorithm you could use
sort objects by z (or keep them sorted by z, or depth buffer tricks etc)
iterate and do a bounds test, stopping when you hit the first one.
This is called Ray Tracing (oops, my mistake, it's actually Ray Casting). Every Physics engine has this functionality. You can look at one of the simplest - ODE, or it's derivative - Bullet. They are open-source so you can take out what you don't need. They both have a handy math library that handles all oftenly needed matrix and vertex operations.
They all have demos on how to do exactly this task.
I suggest you consider looking at this issue from a bigger perspective.
The boxes are just points at a lower resolution. The trick is to reduce the resolution of the mouse to figure out which box it is on.
You may have to perform a 2d to 3d conversion (or vice versa). In most games, the mouse lives in a 2d coordinate world. The stuff "under" the mouse is a 2d projection of a 3d universe.
You want to use a 3D picking algorithm. The idea is that you draw a ray from the user's position in the virtual world in the direction of the click. This blog post explains very clearly how to implement such an algorithm. Essentially your screen coordinates need to be transformed from the screen space to the virtual world space. There's a website that has a very good description about the various transformations involved and I can't post the link due to my rank. Search for book of hook's mouse picking algorithm [I do not own the site and I haven't authored the document].
Once you get a ray in the desired direction, you need to perform tests for intersection with the geometries in the real world. Since you have AABB boxes entirely, you can use simple vector equations to check which geometry intersects the ray. I would say that approximating your boxes as a sphere would make life very easy since there is a very simple sphere-ray intersection test. So, your ray would be described by what you obtain from the first step (the ray drawn in the first step) and then you would need to use an intersection test. If you're ok with using spheres, the center of the sphere would be the point you draw your box and the diameter would be the width of your box.
Good Luck!