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metal: collapse consecutive same-target passes into one encoder #641

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14a7978
metal: collapse consecutive same-target passes into one encoder
Jun 13, 2026
3fd2aa8
Merge branch 'master' into metal-merge-passes
not-fl3 Jun 16, 2026
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52 changes: 48 additions & 4 deletions src/graphics/metal.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -282,6 +282,10 @@ pub struct MetalContext {
/// for `apply_scissor_rect`'s Y-flip + clamp.
current_pass_width: u32,
current_pass_height: u32,
// Bookkeeping for the deferred-end pass-merge in `begin_pass`
// / `end_render_pass`.
current_pass_target: Option<Option<RenderPass>>,
pending_end_encoder: bool,
view: ObjcId,
device: ObjcId,
current_frame_index: usize,
Expand Down Expand Up @@ -375,6 +379,8 @@ impl MetalContext {
render_encoder: None,
current_pass_width: 0,
current_pass_height: 0,
current_pass_target: None,
pending_end_encoder: false,
view,
device,
buffers: vec![],
Expand All @@ -390,6 +396,17 @@ impl MetalContext {
}
}
}

/// Actually call `endEncoding` and clear deferred-end state.
/// `end_render_pass` defers this so consecutive same-target
/// begin/end pairs can collapse into one Metal pass.
fn really_end_encoder(&mut self) {
if let Some(render_encoder) = self.render_encoder.take() {
unsafe { msg_send_!(render_encoder, endEncoding) };
}
self.current_pass_target = None;
self.pending_end_encoder = false;
}
}

impl RenderingBackend for MetalContext {
Expand Down Expand Up @@ -525,6 +542,10 @@ impl RenderingBackend for MetalContext {
unimplemented!()
}
fn texture_generate_mipmaps(&mut self, texture: TextureId) {
// Close any deferred render encoder before opening a blit
// encoder on the same command buffer — Metal asserts
// "encoding in progress" otherwise.
self.really_end_encoder();
let texture = self.textures.get(texture);
// Catch the bug at the call site instead of letting Metal
// assert on `mipmapLevelCount > 1` deep inside the blit
Expand Down Expand Up @@ -1225,6 +1246,22 @@ impl RenderingBackend for MetalContext {

fn begin_pass(&mut self, pass: Option<RenderPass>, action: PassAction) {
unsafe {
// Reuse the deferred encoder if this begin continues the
// same target with a load-style action — collapses the
// per-draw-call begin/end pattern (e.g. macroquad's) into
// one Metal pass, avoiding a store + (for MSAA) resolve
// per draw on tile-based GPUs.
if self.pending_end_encoder
&& self.current_pass_target == Some(pass)
&& matches!(action, PassAction::Nothing)
{
self.pending_end_encoder = false;
return;
}
if self.pending_end_encoder {
self.really_end_encoder();
}

if self.command_buffer.is_none() {
self.command_buffer = Some(msg_send![self.command_queue, commandBuffer]);
}
Expand Down Expand Up @@ -1308,6 +1345,8 @@ impl RenderingBackend for MetalContext {
// });

self.render_encoder = Some(render_encoder);
self.current_pass_target = Some(pass);
self.pending_end_encoder = false;
}
}

Expand All @@ -1317,10 +1356,10 @@ impl RenderingBackend for MetalContext {
"end_render_pass unpaired with begin_render_pass!"
);

let render_encoder = self.render_encoder.unwrap();
unsafe { msg_send_!(render_encoder, endEncoding) };

self.render_encoder = None;
// Defer `endEncoding`; see `begin_pass` for the reuse rule.
// Anything that breaks the merge invariant runs
// `really_end_encoder` first.
self.pending_end_encoder = true;
self.index_buffer = None;
}

Expand Down Expand Up @@ -1352,6 +1391,11 @@ impl RenderingBackend for MetalContext {
}

fn commit_frame(&mut self) {
// Flush the deferred `endEncoding` from the last
// `end_render_pass`.
if self.pending_end_encoder {
self.really_end_encoder();
}
unsafe {
assert!(!self.command_queue.is_null());
let drawable: ObjcId = msg_send!(self.view, currentDrawable);
Expand Down
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