Think of it like Photoshop's opacity slider between two layers: at 0 you see one, at 1 you see the other, anywhere in between you get a blend. Lerp, Linear Interpolation, is that same operation as a shader node. In shaders, the blend factor t can be a constant, a mask texture, an animated value, a dot product result, whatever drives the blend you need.
The math:
result = a * (1 - t) + b * t
t=0 returns A, t=1 returns B. Most shader tools (Unity Shader Graph, Unreal Material Editor, HLSL's lerp()) follow this convention. You may also see it written as a + t * (b - a), mathematically identical, just rearranged.
Watch the range. Lerp has no built-in clamp. If t goes below 0 or above 1, the output extrapolates beyond A or B, colors can exceed 1.0 and blow out, or drop below 0 and behave unexpectedly depending on your output target. For color blends and masks, add a saturate on t before the node. If you're blending direction vectors or deliberately extrapolating, unclamped is fine.
When the transition feels too mechanical, reach for smoothstep instead, it runs t through a smooth curve before the blend, so the result eases in and out rather than crossing at a constant rate.
© 2026 Stefan Groenewoud - All views are my own, not those of my employer.