Clay custom dispatch now uses a union instead of magic marker
This commit is contained in:
Zachary Levy
+80
-37
@@ -754,14 +754,18 @@ measure_text_clay :: proc "c" (
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}
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// Called for each Clay `RenderCommandType.Custom` render command that
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// `prepare_clay_batch` encounters.
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// `prepare_clay_batch` encounters and which is NOT a levlib-managed variant
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// (e.g. `Backdrop_Marker`).
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//
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// - `layer` is the layer the command belongs to (post-z-index promotion).
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// - `bounds` is already translated into the active layer's coordinate system
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// and pre-DPI, matching what the built-in shape procs expect.
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// - `render_data` is Clay's `CustomRenderData` for the element, exposing
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// `backgroundColor`, `cornerRadius`, and the `customData` pointer the caller
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// attached to `clay.CustomElementConfig.customData`.
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// `backgroundColor` and `cornerRadius`. Its `customData` field has been
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// unwrapped from the `Clay_Custom` envelope: it points at the user's own
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// data (the value the user wrote into the `rawptr` variant), not at the
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// `Clay_Custom` itself. If the union was zero-init (no variant set) or
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// `customData` was originally nil, the callback receives nil.
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//
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// The callback must not call `new_layer` or `prepare_clay_batch`.
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Custom_Draw :: #type proc(layer: ^Layer, bounds: Rectangle, render_data: clay.CustomRenderData)
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@@ -771,33 +775,51 @@ ClayBatch :: struct {
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cmds: clay.ClayArray(clay.RenderCommand),
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}
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// Magic-number-tagged struct that user app data points at via Clay's customData field.
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// `prepare_clay_batch` recognizes these and routes them through a backdrop scope automatically.
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// The user populates a `Backdrop_Marker`, points `clay.CustomElementConfig.customData` at it,
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// and the integration walks the command stream, opening/closing scopes around contiguous
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// backdrop runs. Magic-number sentinel chosen over a separate userData flag so the marker
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// type stays self-describing in core dumps and in any non-Odin debugger view of the heap.
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// Discriminated sum of everything `clay.CustomElementConfig.customData` is allowed to point
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// at. levlib-defined variants (currently just `Backdrop_Marker`) are recognized by
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// `prepare_clay_batch` and routed to the appropriate internal path; the `rawptr` variant is
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// the escape hatch for user-defined custom drawing — `prepare_clay_batch` unwraps it before
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// invoking `custom_draw` so the callback sees the user's pointer in `render_data.customData`
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// exactly as if no wrapper were involved.
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//
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// Contract: `customData`, when non-nil, MUST point at storage holding a `Clay_Custom`
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// value. The user owns that storage; its lifetime must span the Clay layout call and the
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// matching `prepare_clay_batch` call. Pointing `customData` at a bare user struct violates
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// the contract — the dispatcher will read its first bytes as a union tag and either route
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// the draw incorrectly or panic on type assertion. There is no recovery path; this is a
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// strict-discipline API by design.
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//
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// Construction notes (Odin implicit-conversion rules):
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// - Backdrop variant: `bd: Clay_Custom = Backdrop_Marker{...}` works directly.
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// Variant-to-union conversion is implicit.
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// - User pointer: `up: Clay_Custom = rawptr(&my_struct)` — the explicit `rawptr(...)` is
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// required because Odin does not chain `^T -> rawptr -> Clay_Custom` implicitly. A bare
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// `up: Clay_Custom = &my_struct` is a compile error.
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Clay_Custom :: union {
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Backdrop_Marker,
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rawptr,
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}
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// Per-primitive parameters for a backdrop blur dispatched through the Clay integration.
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// Embedded as a `Clay_Custom` variant; `prepare_clay_batch` walks the command stream,
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// opens/closes a backdrop scope around contiguous backdrop runs, and feeds these to
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// `backdrop_blur` via `dispatch_clay_backdrop`. The discriminant is the union tag — no
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// in-band magic field needed (compiler-enforced).
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Backdrop_Marker :: struct {
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magic: u32,
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sigma: f32,
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tint: Color,
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radii: Rectangle_Radii,
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feather_ppx: f32,
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}
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// 'BDPT' in big-endian ASCII. Picked for greppability and to be obviously non-zero in
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// uninitialized memory; user code that forgets to set the magic field gets routed through
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// the regular custom_draw path and surfaces as "my custom draw never fired," not as a
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// silent backdrop schedule.
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BACKDROP_MARKER_MAGIC :: u32(0x42445054)
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// Returns true if this Clay render command represents a backdrop primitive.
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// Identified by a magic-number sentinel in the first 4 bytes of customData.
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// Returns true if this Clay render command represents a backdrop primitive — i.e. its
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// `customData` points at a `Clay_Custom` whose active variant is `Backdrop_Marker`.
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is_clay_backdrop :: proc(cmd: ^clay.RenderCommand) -> bool {
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if cmd.commandType != .Custom do return false
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p := cmd.renderData.custom.customData
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if p == nil do return false
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return (^Backdrop_Marker)(p).magic == BACKDROP_MARKER_MAGIC
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_, ok := (^Clay_Custom)(p).(Backdrop_Marker)
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return ok
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}
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// Dispatch a single non-backdrop Clay render command to the appropriate `draw` primitive.
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@@ -918,28 +940,46 @@ dispatch_clay_command :: proc(
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}
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rectangle(layer, bounds, BLANK, outline_color = color, outline_width = thickness, radii = radii)
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case clay.RenderCommandType.Custom: if is_clay_backdrop(render_command) {
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// The walker pre-filters backdrops into `dispatch_clay_backdrop` and never feeds
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// them here; reaching this branch means either the walker logic is broken or the
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// `customData` pointee mutated between the walker's `is_clay_backdrop` check and
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// this re-check (heap corruption / lifetime bug in user-managed customData
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// memory). Both are renderer-level bugs that warrant a hard failure rather than a
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// silently-dropped panel.
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log.panicf(
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"backdrop marker reached dispatch_clay_command; either the prepare_clay_batch walker is misrouting commands or the customData pointee at %p was mutated mid-frame",
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render_command.renderData.custom.customData,
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)
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} else if custom_draw != nil {
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custom_draw(layer, bounds, render_command.renderData.custom)
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} else {
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log.panicf("Received clay render command of type custom but no custom_draw proc provided.")
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case clay.RenderCommandType.Custom:
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// Copy the CustomRenderData by value so we can patch its `customData` field for the
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// user callback without mutating Clay-owned memory. After unwrapping, the callback
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// sees its own pointer in `render_data.customData`, identical to what it would see
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// if `Clay_Custom` did not exist as an intermediary.
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patched := render_command.renderData.custom
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// Default to nil so a zero-init `Clay_Custom` (no variant set) and an originally-nil
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// `customData` both surface to the callback as `customData = nil`.
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patched.customData = nil
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if custom_data_pointer := render_command.renderData.custom.customData; custom_data_pointer != nil {
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switch custom_value in (^Clay_Custom)(custom_data_pointer)^ {
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case Backdrop_Marker: // The walker pre-filters backdrops into `dispatch_clay_backdrop` and never feeds
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// them here; reaching this branch means either the walker logic is broken or the
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// `Clay_Custom` variant tag mutated between the walker's `is_clay_backdrop` check
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// and this re-check (heap corruption / lifetime bug in user-managed customData
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// memory). Both are renderer-level bugs that warrant a hard failure rather than a
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// silently-dropped panel.
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log.panicf(
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"backdrop marker reached dispatch_clay_command; either the prepare_clay_batch walker is misrouting commands or the customData pointee at %p was mutated mid-frame",
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render_command.renderData.custom.customData,
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)
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case rawptr: patched.customData = custom_value
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}
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}
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if custom_draw != nil {
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custom_draw(layer, bounds, patched)
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} else if patched.customData != nil {
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log.panicf(
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"Received clay render command of type custom with non-nil user data but no custom_draw proc provided.",
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)
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}
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}
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}
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// Dispatch a single backdrop Clay render command to `backdrop_blur` on the active layer.
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// Caller guarantees a backdrop scope is open on `layer` so the underlying
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// `append_or_extend_sub_batch` contract assertion is satisfied.
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// Caller guarantees:
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// - a backdrop scope is open on `layer` so the underlying `append_or_extend_sub_batch`
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// contract assertion is satisfied;
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// - the command's `customData` points at a `Clay_Custom` whose active variant is
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// `Backdrop_Marker` (the walker has already verified this via `is_clay_backdrop`).
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//INTERNAL
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dispatch_clay_backdrop :: proc(layer: ^Layer, cmd: ^clay.RenderCommand) {
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bounds := Rectangle {
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@@ -948,7 +988,10 @@ dispatch_clay_backdrop :: proc(layer: ^Layer, cmd: ^clay.RenderCommand) {
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width = cmd.boundingBox.width,
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height = cmd.boundingBox.height,
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}
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marker := (^Backdrop_Marker)(cmd.renderData.custom.customData)
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// Type-asserting form (no `, ok`): panics loudly if the variant tag changed since
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// `is_clay_backdrop`, which is the desired tripwire for a heap-corruption bug in
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// user-managed customData.
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marker := (^Clay_Custom)(cmd.renderData.custom.customData).(Backdrop_Marker)
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backdrop_blur(
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layer,
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bounds,
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