Light Learns to Bounce
Surfaces in Lux now catch the colour of whatever sits next to them. Put a white object beside a red wall and its facing side picks up a warm red blush, the way real light spills off one surface onto the next. It is Lux's first global illumination: indirect, coloured, and aware of which way a surface is pointing.
Stand a white mug next to a red folder on a sunlit desk and look at the side of the mug facing the folder. It is not white there. It has gone faintly pink, lit by red light that hit the folder, gave up on being red paper, and bounced. Every room you have ever been in is full of this quiet second-hand light, and until this release Lux ignored all of it. A surface was lit by the lamps pointing at it and nothing else. Shadows fell to pure black, and a white object next to a red wall stayed obstinately white. This is the post about teaching the light to bounce.
The light that never arrived
Direct lighting is the easy half of the rendering equation: for each lamp, work out how much of it reaches a surface. The hard half is everything that arrives after a bounce, the red the wall throws back, the glow a bright floor lifts into the shadows, the soft fill that makes a room feel like a room instead of a stack of spotlit props. That second-hand light is what artists mean when they say a render looks “flat” or “CG.” Lux had the flat version. Lit faces looked right, but the moment a surface turned away from a lamp it dropped to black, with no sense that it sat in a coloured world.
So Lux now keeps a running picture of the indirect light in a scene. The space around your objects is sampled on a grid, and at each point the engine traces short rays to see what is nearby, catches the light bouncing off those surfaces, and remembers it. When a surface is shaded, it asks that grid what colour light is arriving from its surroundings and adds it in. A white sphere beside a red wall now reads red down the side that faces the wall, fading back to neutral as it turns toward the lamp.
Bouncing in the right direction
The first cut of this stored a single number per point: how much light, total, with no sense of where from. That gives you a soft fill, but it lands as a flat wash, the same blush smeared evenly across a surface no matter which way it faces. A real bounce is directional. The red is strongest where the surface looks straight at the wall and falls away as it turns, the same way the lit side of anything is brightest where it faces the lamp.
So the grid now records not just how much indirect light there is but which direction it comes from, and a surface reads it against the way it is pointing. The blush wraps the facing edge and fades across the body instead of sitting there like a sticker. Alongside that, the stored light is smoothed as it settles, so the result is a clean gradient rather than the grainy speckle that an honest ray-traced estimate starts life as. It is subtle by nature, real colour bleed always is, you have just never consciously noticed it because your eye treats it as “this looks like a real place.” That is rather the point.
And the front door now opens
Getting here turned up an unrelated embarrassment worth owning. Opening a 3D scene in the windowed editor had been drawing a black rectangle, because the window was asking the graphics card for a slightly more modest set of features than the renderer actually needed, and quietly falling back to nothing when they were missing. Closing that gap is what makes any of the above visible in the live app rather than only in test renders. While in there, the editor also learned to open a .lux patch straight from the command line, so you can point Lux at a scene file and have it come up with that scene already loaded.
What it buys you
Drop an object into a coloured scene and it belongs there. The shadowed side of a figure picks up the wall behind it, a bright surface lifts the gloom beneath it, and your shadows stop reading as holes cut out of the frame. It works on everything the single shading path already drives, the same one that lights imported models and hand-built materials alike, so you get the bounce for free on whatever you were already rendering. Lux has gone from lighting objects to lighting the space they sit in.