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Published in Phaser World Issue 124 on 30th July 2018 by Richard Davey   @photonstorm

Redevelopment of the Flat Tint Pipeline and the introduction of textured Graphics.

Welcome to Dev Log 124. This covers all of last weeks Phaser development. Let's dive right in.

Phaser 3 uses different internal batches for WebGL rendering based on the type of Game Object you're using. The main one of those is the Texture Tint Pipeline (TTP) which, as the name implies, is responsible for all Game Objects that use textures: Sprites, TileSprites, Text objects and so on. It was this pipeline that I overhauled for the 3.11 release, which you can read about in Dev Log X.

The Flat Tint Pipeline (FTP) is another pipeline, responsible primarily for the Graphics game object. The name comes from its focus on drawing flat tinted objects, i.e. single color objects with no texture. The pipeline is full of methods such as batchFilledRectangle and batchStrokePath. It's also used by the Camera system. If a Camera has a background color set, or has a Flash or Fade effect running on it, then it uses the Flat Tint Pipeline to draw those rectangles to the viewport.

There are two other pipelines. The Forward Diffuse Light Pipeline (FDLP) is used whenever a Game Object has light effects enabled on it and renders using a normal map bound with the objects texture. The final pipeline is the Bitmap Mask Pipeline (BMP). This pipeline is used specifically for dealing with Bitmap Masks. When the Game Objects are being iterated by the renderer if it finds one with a mask set it will call the beginMask method, which in turn sets everything to be rendered to the mask framebuffer.

There are other steps these two pipelines take that I won't cover in this Dev Log. Suffice to say that invoking any pipeline causes the WebGL renderer to do two important things. First, if a pipeline changes, then the old pipeline is flushed out. Then, once flushed, the new pipeline activates its shaders and gets ready to use them. Both of these actions are expensive in terms of adding to the total number of GPU operations being performed and the number of draw calls.

The term 'flush' means to dump all of the data that has been batched to the GPU and cause a draw call. If you've got say 100 Sprites all using the same texture, and then the display list has a Graphics object on it, it will 'flush' those 100 Sprites out. This means all of their data that has built-up in the batch is sent to the GPU and a draw call is requested.

Imagine a typical RPG game scene with a group of monsters. Each monster is a textured animated Sprite with a health bar above its head and a name below. Your first thought would rightly be "Let's use the Graphics Game Object to draw the health bars!" - after all, it's full of methods like fillRect so seems perfect for the task. You happily proceed to drop in Graphics based health bars but as the monster count increases, the frame rate takes a dive and the amount of GPU calls increases exponentially.

The reason is likely obvious to some of you already. As the renderer works its way through the display list it encounters a monster. First, it finds the Sprite, so it uses the Texture Tint Pipeline. Then it finds the health bar, so it has to swap to the Flat Tint Pipeline, causing the Texture Tint Pipeline to flush and the Flat Tint Pipeline shaders to bind. The moment a pipeline flushes it resets its batch back to zero. All the benefits of building up the data in the batch are gone. Then it finds the monsters name as a Bitmap Text object, so it swaps back to the Texture Tint Pipeline, flushing the Flat Tint one and rebinding its shader. This ping-pong process happens for every single monster in the Scene.

With very little effort on your part, all the benefits of batching are destroyed and WebGL will start struggling (sooner on lower-powered devices than others.) The thing is, you've done nothing wrong. There was no reason you should suspect that using Graphics objects would cause this, yet cause it, it does.

Or at least, it used to.

After I refactored the Texture Tint Pipeline in 3.11 I knew that I would work on the Flat Tint Pipeline next. It exhibited lots of the same problems as the TTP did; namely hundreds of lines of duplicate and sometimes inconsistent code. Originally, I thought I was going to do the same thing as I did with the TTP, which was to just tidy-up the internals, consolidate the most common functions and take advantage of the work I'd done on the Transform Matrix class in 3.11. I started out by doing exactly this. The pipeline became smaller and more unified, relying on a core set of internal methods.

Then I took a look at the shader it was using. It was virtually identical to the shader the Texture Tint Pipeline used. Naturally, I started to think: What if the same shader could be used for them both? If that was possible then it would avoid the whole "pipeline swapping, batch flushing, shader binding" issues that were happening. A few hours of coding later and I had my answer: It worked and it worked great!

Buoyed by this progress I carried on consolidating the methods in the Flat Tint Pipeline. It soon became obvious that there were only really a handful of common methods needed, and one of those was identical to a method already in the Texture Tint Pipeline. The more I tidied things up, the more I realized we didn't need the Flat Tint Pipeline at all. So I merged the few remaining methods into the Texture Tint Pipeline, made one small tweak to the shader and the work was complete.

The net result was well worth the few days development it took. I removed the Flat Tint Pipeline entirely. This is over 1000 lines of code gone and a saving of 42 KB. Obviously, some of that code moved to the Texture Tint Pipeline, but only 300 lines of it, yet all of the previous functionality remains intact. File savings aside, the most important benefit is that mixing textured Game Objects and Graphics objects on the display list no longer causes any problems. They're all adding data to the same batch, they're all using the same shader, so it means the number of WebGL operations and draw calls significantly dropped. Let's have a look at a demo to see the impact of this change.

image

If you watch the above demo for a while you'll see the two bands of elves try to decimate each other. It's simple stuff, only 8 animated sprites, a backdrop, and a health bar each. Let's profile this running under the current version of Phaser (3.11):

image

It's a little tricky to make out if you're looking at the image embeddd in the newsletter - but the important part is that this simple scene is using no less than 19 draw calls and a staggering 218 WebGL operations.

After all the work I did on the Flat Tint Pipeline, let's reprofile the exact same scene under Phaser 3.12 Beta 1:

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Again, it might be hard to tell from the size of the screen shot, but you should immediately see there are far less draws going on (the thumbnails along the bottom) and the list of gl ops is massively smaller:

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218 calls down to just 9. 19 draws down to just 3. That's quite some improvement! You can profile the demo yourself, just use Firefox and it's Canvas Profiling tool and swap between testing the 3.11 build against the dev build. Try it on your own games too. It'd be great to see what impact it has there.

Textured Graphics

Nothing in life is truly 'free' though - so what the cost of making this change to the pipelines? The main one is that the Texture Tint Pipeline had two extra attributes and a uniform bound to its shader that the Flat Tint one didn't have. So, for example, when drawing a filled rectangle it's now sending a little more data to the GPU than before. The benefits of not flushing the batch or swapping shaders far outweigh this data cost. When I realised this it did make me think "What if we used that texture though?", and the Graphics.setTexture method was born.

You can now set a fill texture that will be used when filling shapes in the Graphics object. For example, look at the following code:

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And this is what it looks like when rendered:

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Pretty neat, huh? :) You have control over how the texture and the fill style of the Graphics object are used. The default is to mix the fill color with the texture, as seen in the swirly looking triangles in the picture above. You can also choose to have the color solidly fill in all non-transparent areas of the texture, or have just the texture applied and no color at all (the triangle in the bottom left). As well as using textures you can now also set a gradient fill. It works in the same way as setting a per-vertex tint on a Game Object, with the exact same method arguments. You can see it in the two triangles on the right of the image.

There are limitations to how the texturing and gradients work. Firstly, this a WebGL only feature. Secondly, the texture is not a 'fill pattern'. There is no control over how the texture repeats and it fills the shapes in per triangle or quad. The downside of both the texture and gradient fills becomes apparent if you've got a complex path, or try using it on an arc. WebGL works using triangles, so shapes like circles are actually triangulated during runtime and turned into a series of triangles. This is handled internally using the library Earcut. Each one of these triangles is then textured, or filled, on its own. They're not textured as a collective group, which means you'll get some weird looking results like this:

image

^ probably not what you were expecting, right? I'm happy with this as a limitation for now. Textures and gradients work really well for triangles and rectangles and other paths depending on the result you want. It was a relatively free feature to add as it is part of the shader code anyway, so it made sense to expose it. I'd rather you had the choice to use it or not, rather than lock it down. After all, I'm sure you'll come up with some creative ways to use it and it's entirely optional: You can happily just carry on using normal solid color fills like before.

Shape Game Objects

I've lost count of the number of times people have asked me, or posted to the forum, about how it doesn't work when they add a geometry object such as a Rectangle to the display list. I've always been a bit bemused by this. The Geometry objects clearly live in their own name space and have none of the properties any of the other Game Objects do, so there's no way they would work on the display list.

Yet, if you think about it, it makes sense to be able to do this. I had considered adding a Shape Game Object for a while. A combination of a Geometry object with all the aspects a normal Game Object needs in order to live on the display list. I had ruled this out because of the way the Flat Tint Pipeline previously worked. As you've read above though, this pipeline is now fully integrated into the main one, meaning I can proceed and create a Shape Game Object.

I've not yet decided if this will be in 3.12 or the 3.13 release, but I have sketched out the details of it, and essentially it'll be any of the Geometry objects already supported by Phaser combined with a transform, so you can blast it around the display list like you would any other object. It's a nice side-effect of all the work I've been doing in the renderer this past month that I can now offer features like this and know they won't adversely impact the rendering.

Facebook Instant Games Plugin

If you've been keeping an eye on the repo then you'll notice I have started pushing up all of the Facebook Instant Games plugin code too. At the moment it's hanging directly off the main Game object, exposed in every Scene, but that is purely during development. When I'm finished it'll move to its own global plugin and there will be a new 'Phaser + Instant Games' build available and published, which will be updated with every release of Phaser.

I'm very pleased with development of the plugin so far. The Instant Games API is relatively easy to use as is, but there are definitely areas where it could be made more Phaser friendly, which is exactly what I've been doing.

For example, you can call the method loadPlayerPhoto, provide it with a key, and it'll automatically go and grab the player photo for you and store it within the Phaser Texture Manager under the given key, so you can treat it just like any other asset in your game.

I've also built the Data Manager plugin in, so you can create data values directly and modify them, and they'll be instantly synced with your Facebook app. You just have to use the values like normal and the plugin will take care of ensuring they're saved via the API. The same goes for game stats and session data too.

I also added in really easy-to-use commands like openShare. This will take the key of an image in the Texture Manager along with some text, and will automatically open up a Facebook sharing window, pre-populated with your text and image.

There's lots more coming as well, including really easy ways to handle in-game purchases, video ads and the display of leaderboards. Facebook have been excellent to work with on this project and the finished plugin will be available in the 3.12 release. Of course, if you don't want to use it, it won't add anything to your build size. It's entirely optional. But if you've been thinking about trying out making a Facebook Instant Game, 3.12 will make it easier than any other framework out there.