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diff --git a/doc/libgraphics.ms b/doc/libgraphics.ms index 209094d..2fada71 100644 --- a/doc/libgraphics.ms +++ b/doc/libgraphics.ms @@ -1,14 +1,90 @@ .TL -libgraphics +libgraphics: Design and Implementation +.DA .AU Rodrigo G. López rgl@antares-labs.eu -.AB -To be determined. -.AE .SH -Rendering graph -.PP +Introduction +.LP +.I Libgraphics +is a 3D computer graphics library that provides a way to set up a +scene, fill it up with a bunch of models (with their own meshes and +materials), lights and cameras, and start taking pictures at the user +request. It implements a fully concurrent retained mode software +renderer, with support for vertex and fragment/pixel shaders written +in C (not GPU ones, at least for now), a z-buffer, front- and +back-face culling, textures and skyboxes, directional and punctual +lights, tangent-space normal mapping, ??? +.SH +The renderer +.LP +The +.I renderer +is the core of the library. It follows a +.B "retained mode" +model, which means that the user won't get a picture until the entire +scene has been rendered. Thanks to this we can also clear and swap +the framebuffers without their intervention, they only need to concern +themselves with shooting and “developing” a camera. +.LP +It's implemented as a tree of concurrent processes connected by +.CW Channel s—as +seen in +.B "Figure 1" —, +spawned with a call to +.CW initgraphics , +each representing a stage of the pipeline: +.IP +The +.B renderer +process, the root of the tree, waits on a +.CW channel +for a +.CW Renderjob +sent by another user process, specifying a scene, a camera and a +shader table. It walks the scene and sends each +.CW Entity +individually to the +entityproc. +.IP +The +.B entityproc +receives an entity and splits its geometry equitatively among the +tilers, sending a batch for each of them to process. +.IP +Next, each +.B tiler +gets to work on their subset of the geometry (potentially in +parallel)—see +.B "Figure 2" . +They walk the list of primitives, then for each of them +apply the +.B "vertex shader" +to its vertices (which expects clip space coordinates in return), +perform frustum culling and clipping, back-face culling, and then +project them into the viewport (screen space). Following this step, +they build a bounding box, used to allocate each primitive into a +rasterization bucket, or +.B tile , +managed by one of the rasterizers; this is illustrated in +.B "Figure 3" . +If it spans multiple tiles, it will be copied and sent to each of +them. +.IP +Finally, the +.B rasterizers +receive the primitive in screen space, slice it to fit their tile, and +apply a rasterization routine based on its type (only +.I points , +.I lines +and +.I triangles +are supported). For each of the pixels, a +.B "depth test" +is performed, discarding fragments that are further away. Then a +.B "fragment shader" +is applied and the result written to the framebuffer after blending. .PS .ps 7 circlerad = 0.3 @@ -56,33 +132,10 @@ arrow from Tiler.T1 to Raster.Rn chop .ps 10 .PE .B "Figure 1" : -For a +The rendering graph for a .B 2n processor machine. .SH -The scene -.PP -.PS -.ps 7 -boxwid = 0.5 -boxht = 0.2 -linewid = 0.1 -lineht = 0.2 -box "Scene" -down; line from last box.s; right; line -box "Entity" -down; line from last box.s; right; line -box "Model" -down; line from last box.s; right; line -box "Mesh" -down; line from last box.s; right; line -box "Primitive" -down -line from 2nd last line.s; line; right; line -box "Material" -.ps 10 -.PE -.SH Tile-based rendering .PP .PS @@ -144,7 +197,6 @@ Raster: [ move Rn: circle "rasterizer n" ] with .w at Tiles.e + (0.5,0) -arrow dashed from Tiles.T0.e to Raster.R0.w arrow from Tiles.T1.e to Raster.R1.w arrow from Tiles.Td.e to Raster.Rd.w arrow from Tiles.Tn.e to Raster.Rn.w @@ -153,11 +205,69 @@ arrow from Tiles.Tn.e to Raster.Rn.w .B "Figure 3" : Raster task scheduling. .SH +The scene +.PP +.PS +.ps 7 +boxwid = 0.5 +boxht = 0.2 +linewid = 0.1 +lineht = 0.2 +box "Scene" +down; line from last box.s; right; line +box "Entity" +down; line from last box.s; right; line +box "Model" +down; line from last box.s; right; line +box "Mesh" +down; line from last box.s; right; line +box "Primitive" +down +line from 2nd last line.s; line; right; line +box "Material" +.ps 10 +.PE +.SH Frames of reference .PP Frames are right-handed throughout every stage. .PS .ps 7 - +RFrame: [ + pi = 3.1415926535 + circle fill rad 0.01 at (0,0) + "p" at last circle.c - (0.1,0) + xa = -5*pi/180 + arrow from (0,0) to (cos(xa),sin(xa)) + "bx" at last arrow.end + (0.1,0) + arrow from (0,0) to (0,1) + "by" at last arrow.end - (0.1,0) + za = -150*pi/180 + arrow from (0,0) to (cos(za)+0.1,sin(za)+0.1) + "bz" at last arrow.end - (0.1,0) +] +.ps 10 +.PE +.B "Figure 4" : +Example right-handed rframe. +.SH +Viewports +.PP +.PS +.ps 7 +View: [ + boxwid = 3 + boxht = 2 + box with .nw at (-1,1) + "framebuffer" at last box.s + (0,0.2) + circle fill rad 0.01 at (-1,1) + "p" at last circle.c - (0.1,0) + arrow from (-1,1) to (-1,1) + (1,0) + "bx" at last arrow.end + (0,0.1) + arrow from (-1,1) to (-1,1) - (0,1) + "by" at last arrow.end - (0.1,0) +] .ps 10 .PE +.B "Figure 5" : +Illustration of a 3:2 viewport. |