Welcome to your third month of FX training! In Level 0102: Flame, we covered some fire basics where you saw how to design, animate and treat a simple candle flame. This time we're studying a more full-bodied fire for a medieval style torch. Much more substantial than a candle flame, but not quite as complex as a campfire, this effect is an interesting challenge.
Bigger flames bring more complicated shapes, colour layering, interweaving, twisting, turbulence, breaking and expiry. However, the core physics of this flame are similar to the candle flame that you've already studied. The main thing is that the greater amount of burning creates faster, more lively flames.
Removing incandescence from a flame allows you to see the flames as they are; rising ribbons of particle clouds. The best way to see this for yourself is to look at the shadow of a fire.
Seeing this effect helps you think of fire in a different way. Without the visible glow of combustion it seems even more complex. There's a lot going on in there!
Something you may have noticed is that this fire shadow shares some qualities with the ribbon smoke we did in Level 0103. With a lot more heat and movement in the lower half, there are more cloudy shapes at the top. However, the basics are the same. Fast, hot particles at the source, rising quickly, losing heat, direction and light, finally expiring and dissipating as smoke.
Exercise one
Draw a smoke ribbon from lesson 0103, but this time give it a bit more energy at the source and some cloudy shapes at the top. The whole time you're doing this, imagine it as a fire shadow.
In our work, we're usually concerned only with what can be observed under normal conditions, but in a flame shadow, some invisible physics are revealed! Then, when we see the fire together in the frame with its shadow, it's even more obvious that there's a lot more happening than the naked eye usually perceives. Where we see orange, streaky flames with a bit of smoke, the shadow allows us to see all the heat and particles that otherwise escape our notice.
A great amount of the turbulent shadow effect must be caused by the bending of light through the heat. This is what we know generally as a heat haze, or shimmer; the warping of light through waves of heat.
There are many types of flame, fuel and environmental factors considered when animating fire. For our starting point however, we're studying something you might call "standard". It's a typical yellow-orange flame in a fairly ordinary environment, so there's minimal turbulence and flames rise at a constant speed and rate.
Just like every other effect we've covered so far, and will do so in future, it's always helpful to understand at least some of the physics involved. When designing a common torch flame effect for animation, starting factors to consider are speed, size and direction.
.
As we all know by now, the first rule of fire is that shapes rise continuously as a result of the generated heat. The speed at which they rise depends on the type of flame and the environmental conditions. Even in calm conditions though, because of the heat and turbulence generated within a larger fire, torch flames have more pronounced curl and writhe than the small candle flame.
As flames rise, they die. The strongest, brightest spot in the fire therefore hovers just above the source, and once past that, the flames become weak and thin as they rise toward expiry. The first two-thirds of the overall torch effect consists of what I'd call living flame, as opposed to the top third which is mostly dying flame.
When considering a standard oily flame like a medieval torch, a faster fire may be tall and narrow with many ribbons of flame, like shredded fabric. A slow one on the other hand would be squat with smooth, curvy flames that roll and oscillate like a large candle flame.
.
The size of your fire is proportional to the amount and type of fuel. Traditionally, the fuel is a lump of pitch at the end of the torch. Just like a candle, it's a consistent supply of flammable material that means flame torches have a nice reliable rate of steady burning.
As you'll see in a video demo soon, the flame on the vertical sides of the torch are like a thin aura of combustion, but as they rise, flames merge into something like a single body of fire. When designing, it's good practise to start with an outline as a guide for the approximate size and shape of your torch flame.
.
Exercise two
In the image below are three torches. For each one, just like the outline image (above left) draw a single flame outline that is proportional to the perceived fuel source. Click the image if you'd like to download it for the exercise.
Fig. 3 - Various fuel supplies would have different flame outlines.
When you see non-stylised 2D fire (not counting hokey, amateur attempts) it may be one of a couple of generic types. These may be used to set a mood, or could simply be the preferred style of the animator. The types below can be effective in setting a particular mood, or they may be mixed and matched for variation in a scene or sequence.
This style of flame (right) looks and moves very much like steam, as the flames behave like billowing clouds on their way to disintegration. A cloudy fire feels calmer and less vicious than one with more points and tatters. This design may be well suited to a quiet cavern, or cozy drawing room. Hey if you want to get real soppy, how about a romantic fireside scene with some love hearts in those cloudy shapes?
Probably the most classic fire design in 2D feature film animation is this tattered effect (left), where the ribbony flames have ragged ends combined with flowing curves. While fairly realistic, this design gives an overall stylised wildness to the fire that feels a little dangerous; serious. Set the mood of a villain's lair, or have a dragon breathe these jagged torch flames.
In the Level 0202: Flag you may remember one of the advanced assignments was to create a flag that moves like fire. The reason for this is that fire can often have a flow like rippling cloth. In 2D animation, this is an unusual way of thinking about animating fire, but it makes for stylised simplicity and is well suited to some fire cycles, particularly torches.
.
Whether it's realism or 2-colour cartoony fire, try to avoid the consistent-width band of colour around the outside of a flame. That's an amateur's flame.
Fig.4 - Consistent thickness vs interesting variation
Realistically, as you saw in the shadow footage above, the effect is quite fast, with very little time to study individual shapes. Once again, in animation we build on realism and have the freedom to exaggerate. However, if you're shooting for realism, your flames can be faster.
In the video below where I'm animating two types (cloudy and ribbony) of torch fire at 30fps, you can get a feel for how far the flames move from frame-to-frame. For realistic timing, the finished scenes are on 2s, but could be slowed down to 4s and inbetweened if necessary, for theatrical appeal.
As demonstrated in the videos above, I recommend you animate 1-2 seconds of fire, then towards the end, simply animate back into your first drawing to create a seamless cycle.
Alternatively, if you're making a cycle that needs to be extremely small in file-size, a cheap cycle can be created by designing a fire drawing with built-in regularity, then inbetweening it onto itself, just like you did with ripples and flags in lessons 0201 and 0202.
When you have many cycles of the exact same effect together in a scene, it's very important to offset them. Suppose your scene is a long castle corridor; its walls, lined with torches in sconces. If the fire on every torch moves exactly the same, it'll be distracting and the entire scene will be instantly cheapened. You may have seen animated films or even video games where the same fire cycle is used in every torch and literally the first thing you notice is that every fire is moving exactly the same.
So make an effort to offset the timing of your fires, whether it's candles, torches or any other standalone fire cycle. You can offset them in a number of ways. In a scene full of the same fire cycle, try any, or all of the following:
Exercise three
Using Figure 5 (above) as a guide, animate the lifespan of a single flame with realistic timing. Add appropriate colouring for the flame stages.
Fire has a number of qualities that require specific treatments.
Every flame has these and more characteristics, so the larger the fire, the more complex the treatment can be.
In your design process, the first treatment consideration is generally the colours of the effect. The hotter part of the fire, the part with the most flames mingling and clustering, is the brightest. For this inner core of heat, a very light yellow -almost white- is a good choice for a realistic animation fire.
The further from the hot core, the colder the flame. In order of heat, the colours for an every day torch flame are: white, yellow, orange, red and finally, just as the flame dies and becomes black soot, deep red-brown.
In the earlier animation demo, the colour was a flat yellow. With another layer of white hot flame in front of it, the yellow "body" of the flame would be treated with some transparency and blur, then a thin rim of red near the top of each flame. Once directional blur is applied, the red fades upward nicely to simulate the dying flame tips
If you're going for a flat cartoon-style, you won't be too concerned with realistic treatments. A single layer of linework, painted with a couple of common flame colours may suffice. For anything even semi-realistic and more interesting, you'll want to split your fire up into layers.
Before you start animation, if you know that you'll be using layers for your digital treatments, you can use that to your advantage for animation timing. This is particularly useful if your fire is a cycle. If each layer has a different number of frames, the layer timing will be offset, so the cycle won't appear to repeat itself regularly. For example, consider having an inner hot layer with 24 frames, and a flame "body" of 36 frames.
To really control the appearance, flames that require special treatment should be on their own separate layer. This means that your hottest flames will be on their own layer so a separate glow can be applied. The main body of flame can have its separate treatments such as transparency and directional blur, independent of the hot layer.
In the video below, I'm adding a separate layer for a hot, inner core of flame, and applying glows and directional blurs.
The most commonly useful digital treatments for fire are glow and directional blur, as shown in the previous video. Transparency is also very useful, especially if you can apply a variable transparency. Both Flash and Toonboom have variable transparency. The main issue is that the transparencies will be different on every frame, so it's usually a tedious thing to animate.
Variable blur is also a very useful effect, because it allows you to apply blur to specific parts of something. Therefore it's useful for say a sharp flame with a soft trailing edge. Once again, this effect must be animated frame-by-frame, so it can be tedious. It's good to know it's there if you need it though.
Beginner - Animate a single flame shadow that starts at the source of a torch and weaves its way upward, slowing as it cools and dissipates as soot. Refer to the diagrams in the Design and Timing sections.
Intermediate - Animate a torch loop of your own design for at least 2 seconds. Duplicate this loop and offset it so they appear to be 2 separate cycles.
Advanced - Animate three torch loops of different designs and timing lengths. Each torch should have layers for white core, coloured body. Dissipate the flames into dark smoke ribbons as seen in the flame shadow video
A torch fire is a substantial step up from the candle flame and will help you prepare for larger scale fire effects. This effect can be simplified or complicated but once you have some understanding of the physics and design, you only need some patience to attempt any level of fire complexity.
Good 2D fire is a rare skill and as you become more familiar with it, you'll start to notice amateurish attempts at it everywhere! Maybe that sounds just a bit elitist, but in an age where push-button particle systems are claiming all the fire scenes (and generally making a mess of it), the simple fact is that you've just learned something really special!
