Improved clipping

lua/primitive/core/construct.lua

@@ -98,6 +98,166 @@ local function util_PointMirror( point, origin, normal )
     return point + normal * l * 2
 end
 
+-- Two unit axes spanning the plane the normal defines
+local function util_PlaneBasis( normal )
+    local right
+    if math_abs( normal.z ) < 0.9 then
+        right = vec_getnormalized( vec_cross( normal, Vector( 0, 0, 1 ) ) )
+    else
+        right = vec_getnormalized( vec_cross( normal, Vector( 1, 0, 0 ) ) )
+    end
+
+    return right, vec_cross( normal, right )
+end
+
+-- Andrew's monotone chain over parallel coordinate arrays, returning point indices; collinear and
+-- duplicate points are popped so the kept set stays minimal across clips. `order` must hold 1..count.
+local function util_ConvexHull2D( px, py, count, order )
+    table.sort( order, function( a, b )
+        if px[a] ~= px[b] then return px[a] < px[b] end
+        return py[a] < py[b]
+    end )
+
+    local hull, n = {}, 0
+
+    for i = 1, count do
+        local p = order[i]
+        while n >= 2 and ( px[hull[n]] - px[hull[n - 1]] ) * ( py[p] - py[hull[n - 1]] ) - ( py[hull[n]] - py[hull[n - 1]] ) * ( px[p] - px[hull[n - 1]] ) <= 0 do
+            hull[n] = nil
+            n = n - 1
+        end
+        n = n + 1
+        hull[n] = p
+    end
+
+    local lower = n + 1
+    for i = count - 1, 1, -1 do
+        local p = order[i]
+        while n >= lower and ( px[hull[n]] - px[hull[n - 1]] ) * ( py[p] - py[hull[n - 1]] ) - ( py[hull[n]] - py[hull[n - 1]] ) * ( px[p] - px[hull[n - 1]] ) <= 0 do
+            hull[n] = nil
+            n = n - 1
+        end
+        n = n + 1
+        hull[n] = p
+    end
+
+    hull[n] = nil -- last point repeats the first
+
+    return hull, n - 1
+end
+
+
+-------------------------------
+-- Clips a convex point cloud, keeping the normal side; returns nil if nothing survives.
+-- Crossing every above/below pair catches every cut edge, then the 2d hull drops the interior
+-- chord crossings so the point count stays bounded across clips.
+local function clipConvex( points, planePos, planeNormal )
+    local count = #points
+    local above, dist = {}, {}
+    local kept = {}
+
+    -- Sort the cloud by side, keeping what the normal points toward
+    for i = 1, count do
+        dist[i] = vec_dot( planeNormal, points[i] - planePos )
+        above[i] = dist[i] >= -1e-6
+        if above[i] then kept[#kept + 1] = points[i] end
+    end
+
+    if #kept == 0 then return nil end         -- plane removed the convex
+    if #kept == count then return points end  -- plane missed it, hand back the original
+
+    -- Cross the plane in the plane's 2d frame, as scalars in parallel arrays: pairs number in
+    -- the tens of thousands on a dense cloud, so no tables are made per crossing and Vectors
+    -- are only built for the crossings the hull keeps
+    local right, up = util_PlaneBasis( planeNormal )
+    local rx, uy = {}, {}
+    local below, nbelow = {}, 0
+
+    for i = 1, count do
+        rx[i] = vec_dot( right, points[i] )
+        uy[i] = vec_dot( up, points[i] )
+
+        if not above[i] then
+            nbelow = nbelow + 1
+            below[nbelow] = i
+        end
+    end
+
+    local cutX, cutY, cutI, cutJ, cutF, order = {}, {}, {}, {}, {}, {}
+    local ncuts = 0
+
+    for i = 1, count do
+        if above[i] then
+            local da, xa, ya = dist[i], rx[i], uy[i]
+
+            for k = 1, nbelow do
+                local j = below[k]
+
+                -- da >= 0 > db, so the denominator is positive and frac lands in [0, 1]
+                local frac = math_clamp( da / ( da - dist[j] ), 0, 1 )
+
+                ncuts = ncuts + 1
+                cutX[ncuts] = xa + ( rx[j] - xa ) * frac
+                cutY[ncuts] = ya + ( uy[j] - ya ) * frac
+                cutI[ncuts] = i
+                cutJ[ncuts] = j
+                cutF[ncuts] = frac
+                order[ncuts] = ncuts
+            end
+        end
+    end
+
+    local hull, nhull
+    if ncuts < 3 then
+        -- Fewer than three crossings can't bound a face, so there's no hull to take
+        hull, nhull = order, ncuts
+    else
+        hull, nhull = util_ConvexHull2D( cutX, cutY, ncuts, order )
+    end
+
+    for i = 1, nhull do
+        local cut = hull[i]
+        local a = points[cutI[cut]]
+        kept[#kept + 1] = a + ( points[cutJ[cut]] - a ) * cutF[cut]
+    end
+
+    return kept
+end
+
+-- Applies clip planes ( { pos, normal, seal } ) to a construct result, in place. A plane that
+-- would erase the geometry is skipped, so a primitive is never clipped out of existence.
+local function applyClips( result, clips, physics )
+    for _, clip in ipairs( clips ) do
+        local planePos = clip.pos
+        local planeNormal = clip.normal
+
+        -- Clipping a multi convex will always result in a concave hole in the physics mesh.
+        -- We shouldn't introduce a visual filling where there is a physical hole.
+        local seal = clip.seal and ( not istable( result.convexes ) or #result.convexes <= 1 )
+
+        if physics and istable( result.convexes ) then
+            -- Cut every collision hull, dropping the ones the plane wiped out
+            local clipped = {}
+            for i = 1, #result.convexes do
+                local convex = clipConvex( result.convexes[i], planePos, planeNormal )
+                if convex then clipped[#clipped + 1] = convex end
+            end
+
+            -- Only change if a convex got clipped
+            if clipped[1] then result.convexes = clipped end
+        end
+
+        if CLIENT and istable( result.verts ) and istable( result.index ) then
+            -- Cut the render mesh, capping the hole when the clip asks to be sealed
+            local above = result:Bisect( { pos = planePos, normal = planeNormal }, seal, false )
+            if above then -- false when the plane misses the mesh, in either direction
+                result.verts = above.verts
+                result.index = above.index
+            end
+        end
+    end
+end
+
 
 -------------------------------
 addon.construct = { simpleton = {} }
@@ -192,6 +352,11 @@ do
             return true, errorModel( 4, name )
         end
 
+        -- Cut with any caller-supplied clip planes before Build triangulates, so cut faces get UVs
+        if istable( param.clips ) and param.clips[1] then
+            applyClips( result, param.clips, physics )
+        end
+
         if CLIENT then
             -- Bad vertex table, error model CODE 5
             if not istable( result.verts ) or #result.verts < 3 then

lua/primitive/entities/base.lua

@@ -54,12 +54,39 @@ function class:SetupDataTables()
     self:PrimitiveVar( "PrimMESHPOS", "Vector", { global = true, category = "model", title = "offset", panel = "vector", min = Vector( -500, -500, -500 ), max = Vector( 500, 500, 500 ) }, true )
     self:PrimitiveVar( "PrimMESHROT", "Angle", { global = true, category = "model", title = "rotate", panel = "angle" }, true )
 
+    -- Tell improved clipping we are responsible for maintaining the mesh and its clips.
+    self.ImprovedClippingExternalMesh = true
+
     self:PrimitiveSetupDataTables()
 end
 
 
 function class:PrimitiveGetConstructSimple( name )
     local keys = self:PrimitiveGetKeys()
+
+    -- Bake any improved clips in as entity-local planes.
+    if ImprovedClipping then
+        local clips = ImprovedClipping.GetClips( self )
+
+        if clips[1] then
+            local param = {}
+            for k, v in pairs( keys ) do param[k] = v end
+
+            local planes = {}
+            for i = 1, #clips do
+                local clip = clips[i]
+                planes[i] = {
+                    pos = clip.Normal * clip.Distance,
+                    normal = clip.Normal,
+                    seal = clip.Seal ~= false,
+                }
+            end
+            param.clips = planes
+
+            return Primitive.construct.get( name, param, CLIENT, param.PrimMESHPHYS )
+        end
+    end
+
     return Primitive.construct.get( name, keys, CLIENT, keys.PrimMESHPHYS )
 end
 
@@ -195,6 +222,10 @@ local function rescale( self, scalar )
 end
 
 function class:PrimitiveRebuildPhysics( result )
+    -- Rebuilding a parented primitive would cause issues with the hitbox. Unparent and reparent
+    local parent = SERVER and self:GetParent() or nil
+    if IsValid( parent ) then self:SetParent( nil ) end
+
     local props
     if SERVER then
         props = self:PrimitiveGetProperties()
@@ -254,6 +285,8 @@ function class:PrimitiveRebuildPhysics( result )
 
         self:PrimitiveSetProperties( props )
     end
+
+    if IsValid( parent ) then self:SetParent( parent ) end
 end
 
 
@@ -623,28 +656,13 @@ do
         end
     end)
 
-    -- Re-apply any proper_clipping physics clips after each primitive reconstruction.
-    -- Primitives reinitialize via PhysicsInitMultiConvex on every reconstruction, which wipes the clips
-    -- Bypass the race condition by preserving existing clips on rebuild
-    hook.Add("Primitive_PostRebuildPhysics", "Primitive_ProperClipping", function( ent )
-        if not ent.Clipped or not istable( ent.ClipData ) then return end -- no clips to reapply
-        if not ProperClipping or not isfunction( ProperClipping.ClipPhysics ) then return end -- proper_clipping not installed
-
-        -- Aggregate all physics clips
-        local norms, dists = {}, {}
-        local count = 0
-        for _, clip in ipairs( ent.ClipData ) do
-            if clip.physics then
-                count = count + 1
-                norms[count] = clip.norm
-                dists[count] = clip.dist
-            end
+    -- Rebuild on clip changes so the new planes get baked in ( see PrimitiveGetConstructSimple ).
+    -- The hook only exists when Improved Clipping is installed, so neither addon depends on the other.
+    hook.Add( "ImprovedClipping_ClipsChanged", "Primitive_ImprovedClipping", function( ent )
+        if ent.IsPrimitive and istable( ent.primitive ) then
+            ent:PrimitiveReconstruct()
         end
-
-        if count == 0 then return end -- no physics clips to reapply
-
-        ProperClipping.ClipPhysics( ent, norms, dists, true )
-    end)
+    end )
 end