angelhill.net/code

As I talked yesterday about hierarchies and sounds, all of these things are implemented here.
Hierarchies will be useful for ship formations and large bosses.

Another previously (by me) unseen use of hierarchies is of course for collision detection.
Although it’s probably best to generally let small one piece objects deal with their own collision detection, larger more complex objects will certainly need several bounding boxes or spheres, and they will obviously be children to the object in question. They will pass down collision events to their father.

Right now I am struggling with a little issue here. Torpedoes from my own ship should not be able to hit other torpedoes fired from my own ship. Well torpedoes should not hit torpedoes at all, but if my ship has children, a torpedo fired by me should not be able to hit it (unless otherwise specified of course!)

So far, a child can never harm a parent and vice versa (what a beautiful world!), however a child can harm another child without any trouble (more realistic, less desirable). Of course, one can always go down the tree checking to make sure that both children do not have the same parent, but this might prove troublesome.

One idea might be to provide each object with unique shield frequency. Object that should not hit eachother would have the same frequency. This is a pretty bad idea I think, because torpedoes should not hit other torpedoes, but they should certainly be able to hit other ships.
So that idea falls short. It is a cool idea tho, I might use it for something.

Also, in an ideal hierarchy, each object should be a child of the SUPER OBJECT (in this case, the game world. This would serve a good purpose, such as if the world is moving, it would move all of it’s children. So just because things inherit from the same world, if they can not collide, this is a problem.

An alternative sollution is required.

Here are the variables that need to be considered:
1. Any object should be able to collide with another object
2. Any parent or child should decide if it should collide with its filials.
3. Same as above should decide if the collision will cause damage or do something else
4. Any object should be able to decide whom it can and can not collide with
5. Any object should be able to be out of phase, and thus not collide with anyone.

Solutions to the points:
1. This already works, but might need to be redesigned to accomodate new collision rules.
5. An invisible flag should exist, invisible objects can not collide with anything. Sounds will be invisible.

The other aspects are as of yet unsolved, but they will be in due time. I shall return when I have found a good solution.

Right now I branched my isometric game engine into a sidescrolling spaceshooter ala r-type or ikaruga (you could rotate it to become a sideshooter!).
I am obviously not abandonning the game engine, but at some point I felt that it was getting a bit huge and out of my control, so I had trouble testing new ideas and implementing new features.

Since everything I do in game development and C++ programming is currently my first time, I thought I needed a smaller project to complete, and also a project where I could implement all the features that a game might need. My SpaceShooter is this.

Basicly I need to try tons of different stuff in order to learn it, and the best way to go is to do a few different projects. The SpaceShooter seems simple enough to implement at least on a feature level.

So far I have a ship, which can fire torpedoes, making noises when torpedoes are fired. The torpedoes can hit the computer “controlled” opponent which is flying around the screen and shooting it’s own torpedoes. They can kill it. It also dies if it crashes into you.

Later I will discuss hierarchies and collisions.

I think I got the whole sound thing under control.

I am using OpenAL to play sounds, which means sounds can have vectors to specify velocity and position. This isnt too imporant really since I will probably add the ability to turn off environmental audio. The point is, sounds are now ordinary objects just like you and me. They are labeled not solid so they can never collide with anything, and in order for me to deal with them properly, they are added as children to whatever object produces them.

The only problem I believe I currently have is that the sound objects do not die when the sound is finished, which is not a very nice way to deal with memory

However I am working on that, now that I have dealt with hierarchies. The cool thing about hierarchies is that I can now easily create formations of enemy ships!

I also implemented that thing I talked about in my previous post. There is a method called obeyParent(), which can be overridden by any class inheriting from object, and this method basically takes whatever data the current objects needs to inherit from its father and applies it to itself.

So for a torpedo, this is nothing, and thus the method is empty. The ship uses the default, which is to apply the fathers velocity to the childs position. For the sound, I have not figured it out to 100% yet, but one of the aspects is to set the sounds position to that of its father. I believe i might need to mess with some other stuff because the sound is still not perfect when you move around.

In any case, now its time for bed.

I am now working on building object hierarchies.

First of all, if an object plays a sound, that sound should follow the object’s position (especially when dealing with environmental audio), for this I want to make the sound a part of the object.
But there can be several sounds, and if the object is a robot with 3 arms, you should be able to destroy each arm separately.

The children should inherit properties of their parent, however what properties should be inherited, and which should not?

Obviously the velocity of the father should be the same for all children. Of course, each child can also have its own velocity, and the father’s velocity is simply added to the child’s.

What about hitpoints, and other attributes? The question is if any of these variables should be passed onto the children, and also for example, if the children can survive without their parents. Should this stuff be decided on an object level, or during the joining itself?
Also some children such as torpedoes should certainly not inherit the ship’s velocity.

So this leads me to the conclusion that polymorphism, as always, is the answer.
Each object will have a virtual method for hierarchies, this method will grab whatever attributes the current object wants from its parent. I love coming up with cool ideas out of the blue heh.

There is also the question if children should be part of the object manager or if every father should take responsibility for his children. At this point, I think centralizing basic object management is probably easiest. There is one thing that is important tho, and that is that when a father dies, something has to be done about the children, and the question is if the children can survive without their father or not. I’ll need another lightning bolt to hit me to come up with the solution to that one.

For now, signing off.

In my quest of never being able to decide on something, I am going to get some more abstraction going.

Since my code is very object oriented, I was able to create a second game loop file, which used openGL and drew boxes where game objects were supposed to be. Even the movement worked perfectly.

This is good news because I want to play around with 3D as well as 2D and 3D can also be used to help see things like pathfinding and testing of collision detection, since you can easily draw lines and simple geometric shapes. Who knows, maybe I’ll go with 3D in the end.
The important lesson here is that by modifying the game loop a little to include OpenGL init code and other OpenGL related stuff like rotation (to have an isometric perspective), and removing the loading of sprites (1 line of code) since SDL surfaces do not play with OpenGL, I was able to convert my “game” to a 3D engine.

I plan to continue on this abstract path, basically trying to keep the graphics engine and game objects as separate as possible, so that I can decide later what kind of engine I want to use. Since my main focus right now is on object interaction, I can deal with graphic engines later. And currently, my code allows me to do just that. (well, almost anyway! heh)

I’ve added the ability to target stuff. You click on it, and its targeted.

I had a bit of a problem at first, since when targeting you pass the new target to the targeter, but if the target is deleted, then the targeter still targets it and bad things happen if he tries to do stuff.

So i added a thing which keeps track of who is targeting any mob at any given time, so when the mob is destroyed, it makes sure to set all of its targeteers targets to null, thus eliminating the problem. It still has some minor bugs, but nothing serious.

Now I am working with distances. I need to calculate the distance of one object to another, or more precisely, the vector from one object to another. In itself this is not too difficult, but currently it’s proving to be a challenge because of the architecture I have built for storing coordinates of things.

I am going to read up a bit on 3 dimensional vectors and how to handle them in my physics book hehe. But so far its extremely fascinating. Next I will have to create my own vector class which can do all vector related calculations.

I should try to use vectors for pretty much everything relating to position, since as the physics book puts it: In kinematics, we describe the motion of a particle using vectors to specify its position, velocity and acceleration (I payed a fantastic $176 USD for volume 1 and 2 of these books, plus shipping and fucking taxes). This will be something to do tomorrow. Or maybe later tonight.
Right now I am a little pissed off at the problems with circular dependencies and how to solve them in C++ (object A needs to know about about B, and B needs to know about A, wtf??)
So I am gonna watch some anime to relax…hehe

Next step is to redesign my position classes (Point2D and Point3D) to be more like vectors and matrices, since that’s what we are essentially dealing with…

Oh well.