Vitrail Shaders

Added

• The far terrain of Distant Horizons is drawn by the shader pack itself, lit and fogged like the land it meets. That mod draws its distant land into images of its own and paints only the colour back onto the picture, so no pack ever saw it: no fog on it, a depth of field focused past it, water that did not know it was behind it. Its geometry is now handed to the pack's own dh_terrain and dh_water programs, drawn into the pack's own targets, and its depth is served beside the world's under the names packs read it by, which is the arrangement they are written against. The fog, the shadows and the occlusion on the distant land are the pack's own from there, and the seam where it meets the near terrain closes.

  Two limits worth knowing. A pack that ships no dh_terrain keeps Distant Horizons' own drawing, which no pack effect touches. And the far terrain does not enter the pack's shadow map yet, so what shades it is what the pack computes from its depth rather than a shadow the map carries.

  What this waits on is Distant Horizons and not Vitrail: that mod has to draw on this backend at all, which the version named in INSTALL.md does not, and it has to be one whose insides this engine can read, which the log says when it is not, naming that mod as installed but not in a shape its far terrain can be served from. The log names Distant Horizons as found when it is, and names each far terrain pass as the pack's programs take it over.

• A mob and a piece of armour take the relief their resource pack draws for them. A skin and an armour layer are textures of their own rather than sprites in an atlas, so the maps a material resource pack ships beside them were never read at all and both names came back flat: every mob stayed matte while the terrain around it had relief. They are now read from whichever texture the draw is really using, the same way the atlases already were, and the log names each texture that answers as the skin first comes on screen. A skin downloaded from the skin server rather than shipped by the resource pack has no maps beside it and is left alone.

• A normal map on a mob, on armour or on a chest is read the right way round. The two values a pack works a bump out from, the middle of the sprite a face is mapped to and the direction the texture runs in over it, were the same constant for every face of every piece: a pack lighting a mob through them tilted every bump on it the same way, whichever way the face was really turned. Both are now worked out over each polygon and carried on its corners, on the mobs, on the block entities, on a held item and on the hand alike. Of the hundred and fifty entity programs the eight packs tested ship between them, seventy-five read the sprite middle and sixty-one read the direction. What it changes on screen depends on the resource pack as well: a mob with no normal map beside its skin has nothing to tilt, and finding that map is the entry above.

• A mob flashes again when it is hurt, and a creeper whitens before it goes off. The colour the game lays over a mob it has just damaged was reaching the pack as one number for the whole world, so a pack that paints the flash itself painted nothing: the red hit, the white of a creeper about to explode and the tint on a mob standing in fire all went missing the moment the pack took the mobs over. It is now read off the mesh, one value per vertex, which is where every one of the eight packs tested expects to find it.

• A pack can tell one kind of mob from another again, and a chest from the block it stands in. The three numbers a pack compares against a mob type, a block entity and the item being drawn were reaching it as one value for the whole world, because they were handed over per draw and a draw carries a whole batch of pieces at once. They now ride on the geometry itself, one value per vertex, out of the pack's own entity.properties, block.properties and item.properties. What it changes on screen is whatever the pack wrote on those numbers: the subsurface scattering some packs give to living things alone, the treatment of an end crystal and of its beam. Seven of the eight packs tested read at least one of the three, one of them only in the shadow map; the eighth declares one and never reads it. The lightning bolt is not among them and stays as it was: the game draws it with a mesh this engine does not read.

  The entity mesh only carries the three while the pack is drawing the entities or the hand, so turning either switch now rebuilds the world, exactly as the terrain switch already did. It does not ask for a restart.

• The sky of the End is painted by the pack now, where the game kept its own shader for it. The box of sky and the flash that crosses it both go through the program the format keeps for the textured pieces of the sky, the one that already drew the sun and the moon. Until now that sky was the last piece the game still drew itself: a pack's own sky program never ran in the End, and only its post-processing reached what you saw there. The Nether is the one place left with none of the pack's sky in it, and there the game opens no sky pass at all.

• Glowing eyes are painted by the pack now, where the game kept its own shader for them: the eyes of a spider, an enderman, a phantom, a breeze and the ender dragon, and the bioluminescent parts of a warden, which the game draws the same way. They go through the program the format keeps for eyes alone, and they are added onto the mob's skin rather than laid over it, which is what makes an eye read as a light rather than as a sticker. They are also drawn at full brightness whatever the mob is standing in, as the game draws them: handed the light of the spot instead, a pack that shades by that light would have put out the eyes of anything standing in the dark, which is where they matter most. Six of the eight packs tested ask for that light in the program that serves their eyes, and one of them looks the game's light map up with it, which is where it shows on screen. They reach the pack's shadow map as well, where every draw of them used to be dropped, on the light of the spot rather than at that full brightness. What that puts into the map is colour and not depth, so an eye lays no shadow of its own; what it changes is what a pack reading the map's colour finds there.

• The wind a breeze throws and the swirl over a charged creeper are painted by the pack now, where the game kept its own shader for both. What held them back is a texture matrix of the game's own that scrolls them, and that matrix is answered out of the game's transforms now, so a breeze scrolls rather than sitting frozen on one frame of its offset and two breezes on screen keep their own. The swirl writes every image the pack declares for its entities: on five of the eight packs tested that is between two and four images rather than the single one it would otherwise have reached.

Changed

• A chunk vertex only carries what the pack loaded actually reads. Every vertex of every section used to carry the block id, the middle of the sprite, the offset to the middle of the block, the normal, the tangent and a second copy of the colour, whichever of those the pack asked for: forty four bytes each, whether four of them were read or none. The pack's own chunk programs are now read first and the mesh is built from what they name, so a vertex costs between twenty four and forty bytes. Of the eight packs tested, one drops sixteen bytes a vertex, one twelve, one eight and the other five four. It is video memory and the bandwidth of every chunk draw, so it is paid twice a frame as soon as a shadow map is being filled. Switching between two packs that read different names rebuilds the world, as switching the terrain off already did.

• The normal and the tangent of a chunk vertex travel in one word instead of two. The tangent is at a right angle to the normal, so once the normal is known there is nothing left of it but an angle and the direction the frame turns in, which is how the engine the packs are written against has always stored the pair. That is the last four bytes of the paragraph above, on every pack that lights the terrain by a normal, and it is where the upper bound of forty comes from. A pack reads the same two directions as before: the normal comes back four times closer than it did, and the tangent, which every normal map on the terrain is read through, is now exactly perpendicular to it rather than a few thousandths off, at the price of being up to nine tenths of a degree round the face from where it was.

• The settings screen is the one pack authors already know. It is the screen of the engine packs are written against, ported rather than approximated: the same list of packs with the shaders toggle at its head, the same pages of settings with the value of each in a sunken box beside its name, the same Cancel, Apply and Done, the same buttons and panels drawn from the same texture. A right click walks a value backwards, shift and a click give back the value the pack ships, a slider is dragged and only writes when it is let go, and a setting waiting to be applied is marked in amber. Hovering a setting brings up the pack's own words about it in a panel at the bottom.

• The settings screen is reached from the video settings now, under Vitrail in the list of pages on the left, and the icon this mod used to add to the title screen and the pause menu is gone with it. Both of those menus lead to the video settings already, so it is the same number of clicks from either and it is where anything about how the world is drawn is looked for. The I key and the Config button of the mod list still open the screen as before.

• Closing the screen applies what you changed, where it used to leave without writing. Cancel is the button that throws the changes away, and Apply is the one that writes without closing.

• A pack is dropped straight onto the screen, and a settings file exported and imported through the platform's own file window. Clicking a pack in the list now only selects it, so a folder of eight can be looked through without paying for eight loads; Apply and Done are what make a selection real.

• The eye at the bottom right, and F1, take the screen away so that the world behind it can be looked at while a setting is judged. Escape brings it back.

• The button that reads a pack again is a small circular arrow at the bottom left of the screen, mirroring the eye at the bottom right and, like it, shown in a world only, where it used to be a word on the button row shown everywhere. Editing a pack's shaders by hand and pressing it is still the way to see the change without restarting.

• R reads the pack again without opening anything, which is the key the engine packs are written against binds for it, and the real loop: edit a shader in your editor, come back to the game, press it. The game feeds no key while a screen is open, so from inside the settings screen the button is what reaches it. It says in the chat which of the two happened, and a reading that failed says why, in red.

• The blur behind the settings screen fades out with the screen instead of hanging at full width for half a second after the eye has taken the widgets away and then going out in one frame. How wide the blur is does not come from the screen in this game, only whether there is one, so the fade was fading nothing.

• What this engine has to say and the reference has not, a load that failed, how many settings vitrail/options.txt is holding down and how many passes this backend could not build, is on one line at the bottom left.

Fixed

• Mellow draws instead of showing you the game's own picture. A pass may read a value that the step before it never sends, which a pack gets away with elsewhere and this engine refused: the refusal cost the pass, and a pack cannot lose a pass without losing the whole picture, so what you saw was the game with no shader on it at all. The value is now handed over rather than the pass being thrown away. Mellow is the pack it cost, on one of its lighting passes, and it draws now.

• A pass reading its neighbour's value, which showed as a shader that simply looks wrong. The other half of the same pairing, and the half that said nothing: a value a pass sends on and the next one never asks for used to push everything sent after it one place along, so the pass read the wrong value under the right name. Nothing was refused and nothing was logged, which is what made it hard to see. Sixteen passes across Bliss and Mellow were reading at least one value that way: the enchantment shine under Mellow, and under Bliss the block-breaking crack along with the post-processing steps that carry the sun's direction and the exposure, in every dimension.