Cartoon Fire Effect

Hello, I am looking to achieve a nice looking cartoon fire effect. Similar to what was done in this video for the flame on Charizard.

I believe I could implement that effect in Urho by using the stencil buffer - does anyone have any tips/code for how that can be done? Or any suggestions about how else a similar quality effect could be achieved? It doesn’t need to be super realistic, it just has to be fairly performant (e.g. 50000 particles for one fire is a no) and it should look nice on more than just a black background (a lot of particle fire effects seem to rely on having a dark background).

My other thought for the above effect is that it might be possible to not use the stencil buffer and just add a second UV map to the fire core to get the yellow coloration, though I’ve not looked into the details of how that might work yet.

You could also read the same texture twice, once with UVs shifted and treat green as yellow. Then maybe tone down the yellow based on the fragment’s normal.
In short: Write a shader.

1 Like

A texture to experiment with:

Hereby CC0’d.

1 Like

Using cElapsedTimePS to offset the UVs per channel and a Fresnel factor to tone it down.

1 Like

I agree with @Modanung. This can be easily done with a shader.

Not exactly what the original was, but I think I’m liking it.
FX-Flame

The shader, if anyone wants it (it’s basically just Unlit.glsl)

#include "Uniforms.glsl"
#include "Samplers.glsl"
#include "Transform.glsl"
#include "ScreenPos.glsl"
#include "Fog.glsl"

// Based on Unlit.glsl

varying vec2 vTexCoord;
varying vec4 vWorldPos;
#ifdef VERTEXCOLOR
    varying vec4 vColor;
#endif
varying float vHeight;
varying vec3 vNormal; // So we can only change the color towards the edge of the model
varying float vNdotV; // Camera to world pos
varying float vNdotY;

void VS()
{
    mat4 modelMatrix = iModelMatrix;
    vec3 worldPos = GetWorldPos(modelMatrix);
    gl_Position = GetClipPos(worldPos);
    vTexCoord = GetTexCoord(iTexCoord);
    vWorldPos = vec4(worldPos, GetDepth(gl_Position));
    vNormal = GetWorldNormal(modelMatrix);
	vec3 cameraDir = normalize(worldPos - cCameraPos);
	vNdotV = dot(cameraDir,normalize(vNormal));
	vNdotY = vNormal.y;


    #ifdef VERTEXCOLOR
        vColor = iColor;
    #endif
    
    vHeight = iPos.y;

}

void PS()
{
    // Get material diffuse albedo
    #ifdef DIFFMAP
		#ifdef SHELL
			float h = cElapsedTimePS;
		#else
			float h = 0;
		#endif
        vec4 diffColor = cMatDiffColor * //texture2D(sDiffMap, vTexCoord + vec2(0,2.5*cElapsedTimePS));
				min(texture2D(sDiffMap, vTexCoord + vec2(h,2.5*cElapsedTimePS)) + texture2D(sSpecMap, vTexCoord + vec2(1.3*h,3*cElapsedTimePS)),vec4(1.0,1.0,1.0,1.0));
        #ifdef ALPHAMASK
            if (diffColor.a < 0.5)
                discard;
        #endif
        #ifdef REDMASK
            if (diffColor.r < 0.9) // With 0.5 we get some dark lines at the edges of the flame threads
                discard;
        #endif
    #else
        vec4 diffColor = cMatDiffColor;
    #endif
    
	vec3 normal = normalize(vNormal);
    
    diffColor.g += vHeight*10;
    #ifdef SHELL
		diffColor.g = 0.9*pow(1 - pow(vNdotV,2),0.9);
    #else
		diffColor.g = mix(0.7,1.0,vNdotY)*pow(1 - vTexCoord.x*pow(vNdotV,2),0.9);
    #endif
//     diffColor.g = pow(1 - vTexCoord.x*abs(vNdotV),1);
    diffColor.b = 0;//abs(vNdotV); //normal.z;
//     diffColor.rgb = abs(vec3(vNdotV,0,max(vNdotY,0)));//0.5-0.5*normal;

    #ifdef VERTEXCOLOR
        diffColor *= vColor;
    #endif

    // Get fog factor
    #ifdef HEIGHTFOG
        float fogFactor = GetHeightFogFactor(vWorldPos.w, vWorldPos.y);
    #else
        float fogFactor = GetFogFactor(vWorldPos.w);
    #endif

    #if defined(PREPASS)
        // Fill light pre-pass G-Buffer
        gl_FragData[0] = vec4(0.5, 0.5, 0.5, 1.0);
        gl_FragData[1] = vec4(EncodeDepth(vWorldPos.w), 0.0);
    #elif defined(DEFERRED)
        gl_FragData[0] = vec4(GetFog(diffColor.rgb, fogFactor), diffColor.a);
        gl_FragData[1] = vec4(0.0, 0.0, 0.0, 0.0);
        gl_FragData[2] = vec4(0.5, 0.5, 0.5, 1.0);
        gl_FragData[3] = vec4(EncodeDepth(vWorldPos.w), 0.0);
    #else
        gl_FragColor = vec4(GetFog(diffColor.rgb, fogFactor), diffColor.a);
    #endif
}
3 Likes