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Fix hit-testing inside scissored groups #357

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Fix hit-testing inside scissored groups #357

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106 changes: 70 additions & 36 deletions lib/scenic/view_port.ex
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Original file line number Diff line number Diff line change
Expand Up @@ -790,7 +790,7 @@ defmodule Scenic.ViewPort do
# scan the incoming input list and extract any scene transforms
txs =
Enum.reduce(input, txs, fn
{Scenic.Primitive.Component, script_id, local_tx, _pid, _uid, _local_id}, acc ->
{Scenic.Primitive.Component, script_id, local_tx, _pid, _uid, _local_id, _scissor}, acc ->
Map.put(acc, script_id, {local_tx, name})

_, acc ->
Expand Down Expand Up @@ -1638,11 +1638,11 @@ defmodule Scenic.ViewPort do
defp compile_input(graph)

defp compile_input(%Graph{primitives: primitives}) do
input = comp_input_prim([], 0, primitives[0], primitives, Math.Matrix.identity())
input = comp_input_prim([], 0, primitives[0], primitives, Math.Matrix.identity(), nil)

# compile the requested input types
types =
Enum.reduce(input, [], fn {_mod, _name, _tx, _pid, types, _id}, acc ->
Enum.reduce(input, [], fn {_mod, _name, _tx, _pid, types, _id, _scissor}, acc ->
[types | acc]
end)
|> List.flatten()
Expand All @@ -1651,28 +1651,38 @@ defmodule Scenic.ViewPort do
{:ok, {input, types}}
end

defp comp_input_prim(input, uid, primitive, primitives, tx)
defp comp_input_prim(input, uid, primitive, primitives, tx, scissor)

# skip anything hidden
defp comp_input_prim(input, _uid, %Primitive{styles: %{hidden: true}}, _, _tx), do: input
defp comp_input_prim(input, _uid, %Primitive{styles: %{hidden: true}}, _, _tx, _scissor), do: input

# skip script primitives - no input handlers there
defp comp_input_prim(input, _uid, %Primitive{module: Primitive.Script}, _, _tx), do: input
defp comp_input_prim(input, _uid, %Primitive{module: Primitive.Script}, _, _tx, _scissor), do: input

# it is a group. Calc the local transform if there one, but doesn't go into the
# it is a group. Calc the local transform if there one, but doesn't go into the
# list as a component itself...
defp comp_input_prim(
input,
_uid,
%Primitive{module: Primitive.Group, data: ids, transforms: txs},
%Primitive{module: Primitive.Group, data: ids, transforms: txs, styles: styles},
primitives,
tx
tx,
scissor
) do
# calculate the graph-local transform
local_tx = local_tx(txs, tx)

# if this group has a scissor style, create scissor bounds for children
# scissor is {w, h} and clips to {0, 0, w, h} in the group's local space
child_scissor =
case Map.get(styles, :scissor) do
{w, h} -> {local_tx, w, h}
_ -> scissor
end

# reduce the group
Enum.reduce(ids, input, fn id, inpt ->
comp_input_prim(inpt, id, primitives[id], primitives, local_tx)
comp_input_prim(inpt, id, primitives[id], primitives, local_tx, child_scissor)
end)
end

Expand All @@ -1682,11 +1692,12 @@ defmodule Scenic.ViewPort do
_uid,
%Primitive{module: Primitive.Component, data: {_, _, name}, transforms: txs},
_,
tx
tx,
scissor
) do
# calculate the graph-local transform
local_tx = local_tx(txs, tx)
[{Primitive.Component, name, local_tx, self(), [], nil} | input]
[{Primitive.Component, name, local_tx, self(), [], nil, scissor} | input]
end

defp comp_input_prim(
Expand All @@ -1700,16 +1711,17 @@ defmodule Scenic.ViewPort do
styles: %{input: input_types}
},
_,
tx
tx,
scissor
# ) when is_list(input_types) do
) do
# calculate the graph-local transform
local_tx = local_tx(txs, tx)
[{module, data, local_tx, self(), input_types, id} | input]
[{module, data, local_tx, self(), input_types, id, scissor} | input]
end

# primitives that don't have input set are skipped
defp comp_input_prim(input, _uid, _primitive, _, _tx), do: input
defp comp_input_prim(input, _uid, _primitive, _, _tx, _scissor), do: input

defp local_tx(txs, tx_parent) do
cond do
Expand All @@ -1723,6 +1735,21 @@ defmodule Scenic.ViewPort do
end
end

# Check if a global point is clipped by a scissor rectangle.
# Returns true if the point is OUTSIDE the scissor (i.e. clipped/hidden).
# scissor_tx is the scissor group's accumulated transform within its own graph.
# parent_tx is the transform that maps from the graph's local space to global space.
defp scissor_clips?(nil, _gx, _gy, _parent_tx), do: false

defp scissor_clips?({scissor_tx, w, h}, gx, gy, parent_tx) do
# Compose parent_tx with scissor_tx to get full global transform
global_scissor_tx = Math.Matrix.mul(parent_tx, scissor_tx)
inv = Math.Matrix.invert(global_scissor_tx)
{sx, sy} = Math.Vector2.project({gx, gy}, inv)
# Clipped if outside the scissor rectangle {0, 0, w, h}
sx < 0 or sx > w or sy < 0 or sy > h
Comment on lines +1749 to +1750

@crertel crertel Mar 8, 2026

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Are we sure that the scissor rectangle can't ever be negative in either axis?

end

# coalesce the requested positional input into a single simple list
defp update_positional_input(%{input_lists: input_lists} = state) do
input_positional =
Expand Down Expand Up @@ -1761,47 +1788,54 @@ defmodule Scenic.ViewPort do

# components recurse
defp do_find_hit(
[{Primitive.Component, data, local_tx, _pid, _uid, _id} | tail],
[{Primitive.Component, data, local_tx, _pid, _uid, _id, scissor} | tail],
input_type,
global_point,
{gx, gy} = global_point,
lists,
name,
parent_tx
) do
# calculate the local matrix, which becomes the parent of the component
local_tx = Math.Matrix.mul(parent_tx, local_tx)

# recurse to test the component
case input_find_hit(lists, input_type, data, global_point, local_tx) do
{:ok, _, _, _, _} = hit ->
# Rhere was a hit inside the component. Return result as we are done.
hit

:not_found ->
# if not found, keep going
do_find_hit(tail, input_type, global_point, lists, name, parent_tx)
# if there's a scissor, check the global point is within scissor bounds
# before recursing into the component
if scissor_clips?(scissor, gx, gy, parent_tx) do
do_find_hit(tail, input_type, global_point, lists, name, parent_tx)
else
# calculate the local matrix, which becomes the parent of the component
local_tx = Math.Matrix.mul(parent_tx, local_tx)

# recurse to test the component
case input_find_hit(lists, input_type, data, global_point, local_tx) do
{:ok, _, _, _, _} = hit ->
# There was a hit inside the component. Return result as we are done.
hit

:not_found ->
# if not found, keep going
do_find_hit(tail, input_type, global_point, lists, name, parent_tx)
end
end
end

# actual thing to test against
defp do_find_hit(
[{module, data, local_tx, pid, types, id} | tail],
[{module, data, local_tx, pid, types, id, scissor} | tail],
input_type,
{gx, gy} = gp,
lists,
name,
parent_tx
) do
# calculate the inverse maxtrix of parent_tx x local_tx
# calculate the inverse matrix of parent_tx x local_tx
local_tx = Math.Matrix.mul(parent_tx, local_tx)
invert_tx = Math.Matrix.invert(local_tx)

# project the global point by the inverse matrix
{x, y} = Math.Vector2.project({gx, gy}, invert_tx)

# for this to be a yet, it must be both a valid input type on the primitive
# AND in the primitive itself.
with true <- input_type == :any || Enum.member?(types, input_type),
# for this to be a hit, it must pass the scissor check, be a valid input type
# on the primitive, AND be within the primitive itself.
with false <- scissor_clips?(scissor, gx, gy, parent_tx),
true <- input_type == :any || Enum.member?(types, input_type),
true <- module.contains_point?(data, {x, y}) do
# return the xy in parent coordinate space
inv = Math.Matrix.invert(parent_tx)
Expand All @@ -1815,8 +1849,8 @@ defmodule Scenic.ViewPort do
id
}
else
false ->
# No hit here. Keep going
_ ->
# No hit here (scissor clipped, wrong input type, or outside primitive)
do_find_hit(tail, input_type, gp, lists, name, parent_tx)
end
end
Expand Down
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