Monthly Archives: November 2017

Jetboard Joust Devlog #68 – Ray Of Hope!

I felt the latest weapon deserved a post to itself as it took a bit longer than the others and I’m particularly pleased with the result.

It’s called the ‘Gamma Ray’ and I was deliberately going for a kind of retro 50s sci-fi vibe with it. As with the bulk of the weapons (probably more so), there’s actually very little to coding the mechanics of it – probably around 90% of the development time here was spent on the visuals.

The ‘ray’ effect is all created with a custom shader. At its heart it’s an approximated sine wave (calculated using the smoothstep algorithm) – to get it looking more ‘electric’ I vary the amplitude of the wave at random each cycle.

I had a lot of issues finding a technique for generating random numbers in HLSL that I was happy with. I tried out a couple of algorithmic solutions but none of these seemed to look much good to me. In the end I used a second texture as a ‘noise’ lookup table, I created this texture myself by rendering to a RenderTarget2D in MonoGame so I could be sure the ‘noise’ was perfectly distributed. I’ll probably write a simple tutorial post on this subject and include some PNGs with different type of randomness.

I didn’t like using a consistent wavelength for the shader as it seemed to make things too uniform so I tried varying the wavelength per frame. This looked much better but I ran into an issue where the ‘end’ of the ray looked weird if it didn’t taper out to a point, which it wouldn’t do when there wasn’t an exact number of wave cycles across the length of ray.

I tried fading out the end to get around this – this worked OK but not great and looked weird when the ray ‘collided’ with enemies or buildings. In the end I settled on a solution whereby I taper out both the amplitude and ‘stroke width’ of the wave to zero, this seems to work fine and, even with a fractional amount of cycles, the ray now always tapers out to a nice point!

Lastly I applied a raster effect to the wave (again in HLSL) and overlaid two different rays with wavelengths cycling at different rates. The wavelength of both waves in tweened using a ‘Bounce’ tween algorithm so it seems to cycle regularly but in a fairly non-linear fashion.

The concentric circles at the muzzle of the gun and at the point the ray hits something are created using the geometric shaders I discuss here, though I’ve added a raster effect and a gradual fade out.

Dev Time: 2 days
Total Dev Time: approx 134.5 days

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One Of The First Drafts Of The Raygun Shader

The Finished Raygun Effect

The Gamma Ray In Action

Gamma Ray vs Particle Storm

Jetboard Joust Devlog #67 – Finger On The Pulse

Started on the more space-age weapons this week! Got three done which isn’t bad going I guess, I would have liked to get started on another but, as you’ll see below, I wasn’t happy with one of these and decided to start again from scratch.

I also made a couple of changes to my particle system, the main one was adding the ability to align particles left, right, up or down when they’re drawn. This has added a great deal of flexibility in designing the various particle fx which has been the bulk of the work here.

Plasma Rifle
I wanted the first weapon to be pretty close to the feel of the player’s weapon in Defender or Jet Pac (which was probably based on Defender anyway). The actual logic here is pretty simple, a beam is fired and the ‘back’ of the beam moves at a slower rate to the front. Tweaking the particle fx is what took the time and there are three different particle states here, one for the ‘head’ of the beam, one for the ‘tail’, and one for the rings that are formed around it.

I also went through several iterations of the explosion at the end of the beam, going through a bunch of ideas that looked decent but too ‘geometric’ before settling on the version you see here.

Originally I was just performing collision detection for the ‘head’ of the beam but I found this looked a bit weird when enemies moved into the tail and nothing happened to them. Now I also check to see if an enemy has moved into the tail of the beam and apply a smaller amount of damage if they have (based on the theoretical strength of the beam at that point).

Pulse Cannon
I have very fond memories of the two Turok shooters on N64 and my ‘Pulse Cannon’ is somewhat inspired by the ‘Pulse Rifle‘ in those games. It fires rapid bursts of energy with a short delay between each burst.

The mechanics of this weapon were very simple as it’s just basic projectiles moving in a straight line. Again, what took the time was getting the visuals right. here I have a sprite for the centre of the ‘pulse’ and three different particle generators, one for the ring around the pulse and two for its trail.

The last of this batch of weapons was originally going to be based on the ‘triple blaster’ found in a bunch of ‘bullet hell’ style 2D SHMUPs. I spent almost a day going down this path and tweaking some ok looking ‘fireball’ style projectiles (well, the particles are OK, the sprites in front looking pretty lame) but, when the weapon was finally done, I was left feeling rather disappointed with the result. It just seemed rather bland and lacked anything to differentiate it from the other projectile-based weapons in the game (of which there are many).

So I went back to the drawing-board and instead engineered a weapon that creates an expanding field of energy. Even after about an hour of experimenting I could tell that this was going to be much more effective, and it was. Of course it took a long time tweaking the particles again but there’s only two different generators here so less than the previous two weapons.

I didn’t like the energy field just fading out at full ‘spread’ as I felt this looked a bit weird, so instead I made it contract back to a point which seemed to look pretty cool. The damage done by the field of energy is based on how much of the enemy overlaps the field and how concentrated the field is at that point, focussing the field at the end therefore also has implications in the use of the weapon as it means that damage done is super-concentrated at that point.

I’ll probably re-use the original ‘spreader’ bullets for a bespoke enemy weapon or something later in the game. I suspect I haven’t given up tweaking some of these effects either, particularly the plasma rifle – I like it but there’s still something that’s not quite sitting right with me. I think I may like my original version better in some respects.

Also, ‘spreader’ is a bit of a shite name for a weapon. Sound more like something you use to plaster walls or make a toasted sandwich. Must think of something better.

Dev Time: 4 days
Total Dev Time: approx 132.5 days

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The Original Plasma Rifle

The Current Plasma Rifle

The Pulse Cannon

The Original (Shit) Spreader

The Reworked Spreader

Some Gratuitous Action With The New Weapons

Jetboard Joust Devlog #66 – Out With A Bang!

Well, all the major coding on the conventional weapons is now done so there’s just a few bits and bobs before I move on to the more ‘futuristic’ weapon set.

Firstly, I had to design upgrade UI icons for the weapons I’ve added over the past few weeks. These are 32×32 icons so require more detail than the in-game sprites. I was pretty much a #pixelart noob before starting this game and don’t find this type of drawing easy, one of the reasons I went with a limited colour palette (other than liking the ‘gameboy meets spectrum’ aesthetic) was that it would considerably narrow down my options when it came to the art and thus make the drawing considerably less intimidating. I think that was a good move.

You can see the final icons here – I’m not sure, in retrospect, that a square format was the best format to choose for these as many weapons are much more ‘landscape’ in shape – particularly things like R.P.G.s, making them tough to fit in that space without them looking too spindly and weak.

The other major thing to do was add audio for the new weapons. As with the rest on the in-game FX, I designed all the sounds using the DSI Tempest. I stick mainly to the analog oscillators but also use the digital oscs for noise and (sometimes) a pure sine wave. I really love the Tempest for this type of sound design work, the eight-slot mod matrix makes it incredibly flexible, yet it’s really intuitive to use for a synth that’s so deep. Yeah, there’s a couple of things I really wish it had from a sound design perspective (individual level control over each analog osc and pre/post filter as a modulation target) but overall it’s a beast with just the right balance of flexibility and limitations.

I also used my cheapo Boss RV-100 ‘retro’ digital reverb unit and a couple of plug-ins for (sometimes fairly hardcore) compression and limiting.

Lastly, because I liked the chunky Gatling Gun bullets so much (see previous post) I’ve increased the size of the grenade and R.P.G. rocket. Also added a bit of spin to the grenade when it’s fired.

Getting the conventional weapon set done feels like a bit of a milestone so I’m pleased that’s done! next step – plasma rifle!!

Dev Time: 2 days
Total Dev Time: approx 128.5 days

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Upgrade Icons For The Conventional Weapon Set

Tweaking Sounds On The DSI Tempest

Bigger Grenades With Added Spin!

Jetboard Joust Devlog #65 – Bullet Hell

For the last ‘conventional’ weapon in the set I’ve decided to create an old-fashioned Gatling gun.

‘What’s that?’ I hear you cry – ‘There’s already a Gatling gun in the alpha!’

You’d be right of course, but it’s bothered me for a while that the Gatling gun in the alpha doesn’t really react much like a ‘proper’ Gatling gun. It’s far too ‘polite’ and doesn’t have the all-important ‘wind up’ effect where the speed of fire starts slow but increases to ridiculously fast as you keep the trigger held. I remember particularly enjoying the Gatling gun in the underrated ‘Bulletstorm‘.

I’m still keeping the ‘old’ Gatling gun but this will be renamed ‘Uzi 9mm’ which seems more fitting for the way it operates.

Actually coding the ‘new’ Gatling gun was pretty straightforward. As usual I spent most of the time tweaking explosions and the particle effects for the muzzle flash and the bullet trail. For the muzzle flash I’m using a new geometric shader type called ‘burst’ based on offset circles. I was particularly pleased with the bullet explosions and will probably re-use this effect elsewhere in the game (maybe on a much larger scale for some real ‘oomph).

The gun gradually gets faster and more inaccurate as you hold down the trigger. It also recoils pretty badly. I’ve opted for super-big bullets which I think kind-of work (I think they’re funny anyway) even if they’re ridiculously big.

The bullets are the first time I’ve used sprite rotation in the game. I was a bit worried this would look out of keeping with the visual style (as the rotation is done at ‘full’ res rather than the game’s pixel resolution) but it seems to work fine.

So I’m pretty much done with the ‘conventional’ weapons now – just have to add sound FX for this one, the flamethrower, R.P.G. and grenade launcher.

Dev Time: 1.5 days
Total Dev Time: approx 126.5 days

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The Original Gatling Gun – Now Re-christened Uzi 9mm

New Geometric Shader – ‘Burst’
Repeat Fire Takes A While To Get Going

Does Jetboard Joust Now Qualify As A ‘Bullet Hell’ Game?

Some Gratuitous Gatling Action

Jetboard Joust Devlog #64 – Rocket Science

Another day, another piece of overpowered weaponry. And on it goes…

This week’s project has been to add an R.P.G. And of course in this context that stands for ‘Rocket-Propelled Grenade’ rather than ‘Role Playing Game’.

In theory the R.P.G. is a very straightforward weapon to code. Shoot a projectile in a straight line that explodes when it hits something – job done. There’s nothing particularly complex about the mechanics of it at all.

What took the time in practice was tweaking the visuals. Because the R.P.G is a powerful weapon it needs to have a certain ‘wow’ factor attached, consequently I spent considerably more time animating the rocket’s travel and detonation than I have for any other projectile in the game.

When in flight the rocket has a spin animation and two particle generators, one that leaves a ‘thrust trail’ and one that generates a ‘flare’ at the rocket’s exhaust. For the explosions I made use of my new geometric shaders described in this post.

Another difference to other weapons is that the rocket is displayed ‘loaded’ into the launcher before it is fired. This means I have to cope with the scenario where the user is out of ammo (no rocket displayed) and also create an animation for when the next rocket loads. None of this was particularly complicated but it necessitated some changes in the way I deal with weapon attachments for the jetboard.

One area where the mechanics of the R.P.G. needed a bit of specialised treatment was in the distribution of damage when the rocket explodes. I had been working on a similar principle to the bombs and grenades in that damage would be applied equally around the rocket depending on how far away the enemy/player is. The problem with this was that, as the rocket detonates with a very powerful explosion, it was simply too easy to commit suicide by firing into a building or opponent at close range. To rectify this I created a kind of ‘safety zone’ behind the rocket. Characters positioned directly behind the rocket take significantly less damage, characters behind but above or below the rocket are still offered some protection but less so depending on how far away they are. You still have to be careful firing R.P.G.s when you’re low on health though!

Dev Time: 2 days
Total Dev Time: approx 125 days


Early Stages – Muzzle Flash And Recoil To Give The R.P.G. More ‘Heft’

The R.P.G. Flight In Slow Motion

Working On The Explosions

Be Careful Using High Explosives When Your Health Is Low

Jetboard Joust Devlog #63 – Geometric Pixel Shader Tutorial

Been spending the last couple of days working on some geometric pixel shaders that I can use for various in game lighting effects to further juice up my explosions etc.

These may well be of use to others so I thought I’d get them into a serviceable state and do a mini-tutorial on their usage. OK, maybe ‘tutorial’ is too grand a word but I’ve commented the code thoroughly at least! Links to the HLSL source files for these shaders are included at the bottom of this article (scroll down).

I’m assuming the reader has a basic knowledge of HLSL – if not then there’s an excellent introductory tutorial here.

The shaders provided both draw a user-defined number of concentric shapes. The stroke width and spacing between the shapes can be set via user-defined parameters, as can the amount the spacing and stroke width increases at each iteration.

A parameter ‘multiply_increments’ allows the user to set whether the spacing/stroke width increment as applied linearly (by addition) or exponentially (by multiplication).

The supplied texture is used to draw the shapes (I often use a 2×2 white square), a user-defined tint can be applied to this.

All sizes, widths etc are calculated as a proportion of the texture size so usually between 0.0f and 1.0f though you can go larger than 1.0f if you wish some of your outer shape to be drawn outside of the texture (and therefore cropped).

Setting the shader parameters from your .net code would look something like the code below. Adjust these parameters over time to get the kind of trippy effects you see in some of the example GIFs. Maybe you could smooth these parameter changes using LERPing?

Two Geometric Shaders Overlaid
Microsoft.Xna.Framework.Graphics.Effect shader = Game.Content.Load (“circles”);

// The tint that will be applied to the texture – set all values
// to 1.0 to leave the texture untouched
Microsoft.Xna.Framework.Vector4 tint;
tint.W = 1.0f; // alpha – 0.0f – 1.0f
tint.X = 1.0f; // red – 0.0f – 1.0f
tint.Y = 1.0f; // green – 0.0f – 1.0f
tint.Z = 1.0f; // blue – 0.0f – 1.0f
shader.Parameters [“tint”].SetValue(tint);

// The size of the first shape to be drawn
shader.Parameters [“size”].SetValue ( 1.0f );

// The stroke width of the first shape to be drawn
shader.Parameters [“strokewidth”].SetValue ( 0.1f );

// The initial spacing between shapes
shader.Parameters [“spacing”].SetValue ( 0.1f );

// The number of shapes
shader.Parameters [“repeats”].SetValue ( 3 );

// The amount by which spacing increases for each consecutive shape drawn
shader.Parameters [“spacing_increment”].SetValue ( 0.0f );

// The amount by which stroke width increases for each consecutive shape drawn
shader.Parameters [“strokewidth_increment”].SetValue ( 0.0f );

// Whether the spacing/stroke width increment as applied linearly (by addition)
// or exponentially (by multiplication).
shader.Parameters [“multiply_increments”].SetValue ( false );

// Adjust depending on how you’re doing your rendering
SpriteBatch.Begin (…);
shader.CurrentTechnique.Passes[0].Apply ();
SpriteBatch.End (…);

Probably also worth mentioning are the settings required to get the ‘endless loop’ effect you see in these GIFs. It’s pretty straightforward if the spacing and stroke width of shapes is consistent, but if not you need to tween the strokewidth and spacing so that they are the same for the second shape at the end of the loop as they were for the first shape at the start of the loop. It took me a while to get my head round this.

The code below shows some example values – don’t try and cut/paste this as it uses my own tweening classes and a wrapper class for the shader itself. It should be good enough to get an idea of how to set things up though…

// Initial stroke width relative to texture size
float width = 0.0025f;

// My wrapper class for the shader
shader = GeometryShader.CircleShader ();

// Used by my wrapper class – the size I’m drawing the texture on screen
shader.ScaleX = 506;
shader.ScaleY = 506;

// Set up initial spacing and stroke width for the shader
shader.Spacing = width;
shader.StrokeWidth = width;

// Spacing and stroke width will increase by 50% for each concentric shape drawn
shader.SpacingIncrement = 1.5f;
shader.StrokeWidthIncrement = 1.5f;
shader.MultiplyIncrements = true;

// Sets up the values to tween the size of the outer shape over a 30 frame seamless loop
// First two values are the start and end size
shader.TweenSize = new Tween (1.0f, 1.0f + shader.Spacing/shader.SpacingIncrement + shader.StrokeWidth/shader.StrokeWidthIncrement, 30, Tween.Linear);

// Sets up the values to tween the spacing over a 30 frame seamless loop
// First two values are the start and end spacing
shader.TweenSpacing = new Tween (width, width / shader.SpacingIncrement, 30, Tween.Linear);

// Sets up the values to tween the stroke width over a 30 frame seamless loop
// First two values are the start and end stroke width
shader.TweenStrokeWidth = new Tween (width, width / shader.StrokeWidthIncrement, 30, Tween.Linear);

And here are the actual HLSL source files. Note that I am pretty much a beginner at this stuff myself so I make no guarantees as to the suitability of this code for any purpose and I would welcome any contributions towards making it execute more efficiently.

I have plans to add more shape types at a later stage and combine these into one uber-shader that also also shapes to be combined in different ways. Watch this blog for updates…

circles.fx | squares.fx

If this is of use to you I’d welcome more followers on Twitter.

Dev Time: 2 days
Total Dev Time: approx 123 days


Two Circle Shaders Slightly Offset

Square Shader With Additional Rotation Applied