8000 metal: flip + clamp scissor against the active render pass extent by benface · Pull Request #643 · not-fl3/miniquad · GitHub
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metal: flip + clamp scissor against the active render pass extent #643

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Merged
not-fl3 merged 1 commit into from
Jun 15, 2026
Merged

metal: flip + clamp scissor against the active render pass extent #643

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58 changes: 44 additions & 14 deletions src/graphics/metal.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -270,6 +270,10 @@ pub struct MetalContext {
command_queue: ObjcId,
command_buffer: Option<ObjcId>,
render_encoder: Option<ObjcId>,
/// Active pass's color-attachment dimensions in pixels — pivot
/// for `apply_scissor_rect`'s Y-flip + clamp.
current_pass_width: u32,
current_pass_height: u32,
view: ObjcId,
device: ObjcId,
current_frame_index: usize,
Expand Down Expand Up @@ -361,6 +365,8 @@ impl MetalContext {
command_queue,
command_buffer: None,
render_encoder: None,
current_pass_width: 0,
current_pass_height: 0,
view,
device,
buffers: vec![],
Expand Down Expand Up @@ -412,12 +418,25 @@ impl RenderingBackend for MetalContext {
fn apply_scissor_rect(&mut self, x: i32, y: i32, w: i32, h: i32) {
assert!(self.render_encoder.is_some());

let (_, screen_height) = crate::window::screen_size();
// Flip against the active pass height, not the screen —
// they diverge for off-screen targets at high DPI. Then
// clamp into `[0, pass_size]` on both axes: callers
// (macroquad) can briefly request a scissor sized against
// a stale screen cache (e.g. mid-rotation, where the
// caller's `screen_size()` lags MTKView's drawable
// dimensions by a frame), and an unclamped scissor would
// trip Metal validation.
let pass_width = self.current_pass_width as i32;
let pass_height = self.current_pass_height as i32;
let x_clamped = x.clamp(0, pass_width);
let y_metal = (pass_height - (y + h)).clamp(0, pass_height);
let w_clamped = (pass_width - x_clamped).clamp(0, w.max(0));
let h_clamped = (pass_height - y_metal).clamp(0, h.max(0));
let r = MTLScissorRect {
x: x as _,
y: (screen_height as i32 - (y + h)) as u64,
width: w as _,
height: h as _,
x: x_clamped as u64,
y: y_metal as u64,
width: w_clamped as u64,
height: h_clamped as u64,
};
unsafe { msg_send_![self.render_encoder.unwrap(), setScissorRect: r] };
}
Expand Down Expand Up @@ -1158,14 +1177,23 @@ impl RenderingBackend for MetalContext {
self.command_buffer = Some(msg_send![self.command_queue, commandBuffer]);
}

let (descriptor, _, _) = match pass {
let (descriptor, width_px, height_px) = match pass {
None => {
let (screen_width, screen_height) = crate::window::screen_size();
(
msg_send_![self.view, currentRenderPassDescriptor],
screen_width as f64,
screen_height as f64,
)
// Read dimensions from the actual pass attachment
// texture, not `screen_size()`. MTKView's
// `drawableSize` and our cached screen size can
// both transition to the new size one frame before
// `currentDrawable`'s texture is recreated; reading
// the attachment directly avoids the gap.
let descriptor: ObjcId =
msg_send_![self.view, currentRenderPassDescriptor];
let color_attachments: ObjcId = msg_send_![descriptor, colorAttachments];
let attachment: ObjcId =
msg_send_![color_attachments, objectAtIndexedSubscript: 0];
let texture: ObjcId = msg_send_![attachment, texture];
let width: u64 = msg_send![texture, width];
let height: u64 = msg_send![texture, height];
(descriptor, width as u32, height as u32)
}
Some(pass) => {
let pass = &self.passes[pass.0];
Expand All @@ -1180,12 +1208,14 @@ impl RenderingBackend for MetalContext {

(
pass.render_pass_desc,
self.textures.get(texture).params.width as f64,
self.textures.get(texture).params.height as f64,
self.textures.get(texture).params.width,
self.textures.get(texture).params.height,
)
}
};
assert!(!descriptor.is_null());
self.current_pass_width = width_px;
self.current_pass_height = height_px;

let color_attachments = msg_send_![descriptor, colorAttachments];
let color_attachment = msg_send_![color_attachments, objectAtIndexedSubscript: 0];
Expand Down
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