Function write_polyline_triangles

src/plot_renderer/shader.rs:1755–1813

(
    writer: &mut VertexWriter,
    segs: &mut Vec<LineSegment>,
    polyline: PolylineRef<'_>,
    style: LineRenderStyle,
)

            let mut pass = params.encoder.begin_render_pass(&RenderPassDescriptor {
                label: Some("selection overlay"),
                color_attachments: &[Some(msaa_attachment(msaa_targets, LoadOp::Load))],
                depth_stencil_attachment: None,
                occlusion_query_set: None,
                timestamp_writes: None,
            });

            // Set viewport and scissor for selection overlay as well
            pass.set_viewport(x, y, width, height, 0.0, 1.0);
            pass.set_scissor_rect(
                params.clip_bounds.x,
                params.clip_bounds.y,
                params.clip_bounds.width,
                params.clip_bounds.height,
            );

            pass.set_pipeline(pipeline);
            // Draw selection if present
            if let Some(vb) = &self.buffers.selection {
                pass.set_vertex_buffer(0, vb.buffer.slice(..));
                pass.draw(0..vb.vertex_count, 0..1);
            }
            // Draw highlight mask boxes if present
            // Each mask box is a quad (4 vertices) in TriangleStrip topology
            if let Some(vb) = &self.buffers.highlight {
                pass.set_vertex_buffer(0, vb.buffer.slice(..));
                // Draw each quad separately (4 vertices per quad)
                let quad_count = vb.vertex_count / 4;
                for i in 0..quad_count {
                    pass.draw(i * 4..(i + 1) * 4, 0..1);
                }
            }
        }

        // Crosshairs overlay (using line list topology)
        if let (Some(pipeline), Some(vb)) = (
            self.pipelines.line_overlay.as_ref(),
            &self.buffers.crosshairs,
        ) {
            let mut pass = params.encoder.begin_render_pass(&RenderPassDescriptor {
                label: Some("crosshairs overlay"),
                color_attachments: &[Some(msaa_attachment(msaa_targets, LoadOp::Load))],
                depth_stencil_attachment: None,
                occlusion_query_set: None,
                timestamp_writes: None,
            });

            // Set viewport and scissor for crosshairs overlay
            pass.set_viewport(x, y, width, height, 0.0, 1.0);
            pass.set_scissor_rect(
                params.clip_bounds.x,
                params.clip_bounds.y,
                params.clip_bounds.width,
                params.clip_bounds.height,
            );

            pass.set_pipeline(pipeline);
            pass.set_vertex_buffer(0, vb.buffer.slice(..));
            pass.draw(0..vb.vertex_count, 0..1);