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BrainRenderer

Namespace: DISP3DLIB  ·  Library: 3D Display Library

#include <disp3D/brainrenderer.h>

class DISP3DLIB::BrainRenderer

BrainRenderer handles the low-level RHI rendering logic, managing pipelines, shaders, and draw calls for brain surfaces.

Qt RHI-based 3-D renderer managing scene objects, lighting, camera, and render pipeline for brain visualization.

Public Methods​

BrainRenderer()​

Default Constructor.

~BrainRenderer()​

Destructor.

initialize(rhi, rp, sampleCount)​

Initialize resources (shaders, pipelines) for the given RHI and render pass.

Ensures pipelines for all supported modes are created.

Parameters:

  • rhi : *QRhi ** Pointer to QRhi instance.

  • rp : *QRhiRenderPassDescriptor ** Render pass descriptor.

  • sampleCount : int MSAA sample count.

ensureRenderTargets(rhi, colorTex, pixelSize)​

Create the dual render-target pair for multi-pass rendering.

Both render targets share the same color texture and depth-stencil buffer but differ in their load/store flags:

  • m_rtClear: clears color+depth on beginPass (first pass)
  • m_rtPreserve: preserves previous output (passes 2+)

Qt bakes these flags into native resources at create() time, so calling setFlags() dynamically does NOT work (especially on WebGL). This is the validated pattern from test_wasm_multi_pass.

Parameters:

  • rhi : *QRhi ** QRhi instance.

  • colorTex : *QRhiTexture ** Color texture (owned by QRhiWidget or caller).

  • pixelSize : const QSize & Render target dimensions.

rtClear()​

Returns:

  • *QRhiRenderTarget ** — The clearing render target (pass 1).

rtPreserve()​

Returns:

  • *QRhiRenderTarget ** — The preserving render target (passes 2+).

newFrame()​

Start a new frame: frees all per-draw uniform slots.

Call before the frame's first prepare call.

A frame is recorded in two phases. First every prepare*() call writes its uniforms and uploads into resource update batches. Then beginFrame() commits them, and the issue*() calls only bind and draw: QRhi forbids resource updates inside a render pass, and prepare calls made inside one are rejected with a warning.

The renderer owns the GPU copies of the renderables' streams. They are created on the first draw, updated when a stream's generation changes, and freed once the renderable is destroyed or has not been drawn for a while.

cachedMeshCount()​

Returns:

  • int — Number of renderables whose GPU copies the renderer currently holds.

beginFrame(cb, updates)​

Begin the first render pass of a frame.

Clears color and depth.

Parameters:

  • cb : *QRhiCommandBuffer ** Command buffer to record to.

  • updates : *QRhiResourceUpdateBatch ** Resource updates to commit before the pass, or nullptr.

beginPreservingPass(cb, updates)​

Begin an additional render pass that preserves previous output.

Uses the internal preserving render target (m_rtPreserve).

Parameters:

  • cb : *QRhiCommandBuffer ** Command buffer.

  • updates : *QRhiResourceUpdateBatch ** Resource updates to commit before the pass, or nullptr.

prepareSurfaceDraw(u, data, surface)​

Upload the surface's streams if they changed and write the uniforms of one surface draw.

Parameters:

  • u : *QRhiResourceUpdateBatch ** Resource update batch, committed before the pass.

  • data : const SceneData & Scene uniforms (MVP, light, etc).

  • surface : *BrainSurface ** Pointer to surface.

Returns:

  • int — Uniform buffer offset for this draw, or -1 on failure.

issueSurfaceDraw(cb, surface, mode, uniformOffset)​

Draw a surface with the uniforms from prepareSurfaceDraw().

Call inside a pass.

Parameters:

  • cb : *QRhiCommandBuffer ** Command buffer.

  • surface : *BrainSurface ** Pointer to surface to draw.

  • mode : ShaderMode Shader mode.

  • uniformOffset : int Offset returned by prepareSurfaceDraw().

prepareDipoleDraw(u, data, dipoles)​

Upload the dipoles' streams if they changed and write the uniforms of their draw.

Parameters:

  • u : *QRhiResourceUpdateBatch ** Resource update batch, committed before the pass.

  • data : const SceneData & Scene uniforms.

  • dipoles : *DipoleObject ** Pointer to DipoleObject.

Returns:

  • int — Uniform buffer offset, or -1 when nothing is drawn.

issueDipoleDraw(cb, dipoles, uniformOffset)​

Draw dipoles as instanced cones.

Call inside a pass.

Parameters:

  • cb : *QRhiCommandBuffer ** Command buffer.

  • dipoles : *DipoleObject ** Pointer to DipoleObject.

  • uniformOffset : int Offset returned by prepareDipoleDraw().

prepareNetworkDraw(u, data, network)​

Upload the network's streams if they changed and write the uniforms of its draws.

Parameters:

  • u : *QRhiResourceUpdateBatch ** Resource update batch, committed before the pass.

  • data : const SceneData & Scene uniforms.

  • network : *NetworkObject ** Pointer to NetworkObject.

Returns:

  • int — Uniform buffer offset, or -1 when nothing is drawn.

issueNetworkDraw(cb, network, uniformOffset)​

Draw a connectivity network: instanced node spheres and edge cylinders.

Call inside a pass.

Parameters:

  • cb : *QRhiCommandBuffer ** Command buffer.

  • network : *NetworkObject ** Pointer to NetworkObject.

  • uniformOffset : int Offset returned by prepareNetworkDraw().

preparePolylineDraw(u, data, polyline)​

Upload the polyline's streams if they changed and write the uniforms of its draw.

Parameters:

  • u : *QRhiResourceUpdateBatch ** Resource update batch, committed before the pass.

  • data : const SceneData & Scene uniforms.

  • polyline : *PolylineObject ** Pointer to PolylineObject.

Returns:

  • int — Uniform buffer offset, or -1 when nothing is drawn.

issuePolylineDraw(cb, polyline, uniformOffset)​

Draw a polyline as connected segments.

Call inside a pass.

Parameters:

  • cb : *QRhiCommandBuffer ** Command buffer.

  • polyline : *PolylineObject ** Pointer to PolylineObject.

  • uniformOffset : int Offset returned by preparePolylineDraw().

prepareElectrodeDraw(u, data, electrodes)​

Upload the electrodes' streams if they changed and write the uniforms of their draws.

Parameters:

  • u : *QRhiResourceUpdateBatch ** Resource update batch, committed before the pass.

  • data : const SceneData & Scene uniforms.

  • electrodes : *ElectrodeObject ** Pointer to ElectrodeObject.

Returns:

  • int — Uniform buffer offset, or -1 when nothing is drawn.

issueElectrodeDraw(cb, electrodes, uniformOffset)​

Draw electrode lead bodies and contacts, opaque and depth-tested.

Call inside a pass.

Parameters:

  • cb : *QRhiCommandBuffer ** Command buffer.

  • electrodes : *ElectrodeObject ** Pointer to ElectrodeObject.

  • uniformOffset : int Offset returned by prepareElectrodeDraw().

prepareVideoOverlay(rhi, u, overlay)​

Prepare live video overlay GPU resources and upload the latest frame.

Must be called before a render pass starts. Texture uploads require a blit encoder on Metal and must not be recorded while a render encoder is active.

Parameters:

  • rhi : *QRhi ** QRhi pointer.

  • u : *QRhiResourceUpdateBatch ** Resource update batch owned by the caller.

  • overlay : *VideoOverlay ** Pointer to VideoOverlay; ignored when null/disabled.

prepareVideoOverlayDraw(u, data, overlay, surface)​

Write the uniforms of one video overlay draw: a camera-facing quad at the focus position, or, with a target surface, a decal projected onto that mesh.

Call after prepareVideoOverlay().

Parameters:

  • u : *QRhiResourceUpdateBatch ** Resource update batch, committed before the pass.

  • data : const SceneData & Scene uniforms (MVP, camera position).

  • overlay : *VideoOverlay ** Pointer to VideoOverlay; ignored when null/disabled.

  • surface : *BrainSurface ** Target surface mesh (typically scalp/head), or nullptr for the quad.

Returns:

  • int — Uniform buffer offset for this draw, or -1 when nothing is drawn.

issueVideoOverlayDraw(cb, overlay, surface, uniformOffset)​

Draw a video overlay prepared with prepareVideoOverlayDraw().

Call inside a pass.

Parameters:

  • cb : *QRhiCommandBuffer ** Command buffer.

  • overlay : *VideoOverlay ** Pointer to VideoOverlay.

  • surface : *BrainSurface ** Same target surface as in prepareVideoOverlayDraw().

  • uniformOffset : int Offset returned by prepareVideoOverlayDraw().

prepareSlice(rhi, u, slice, slotIndex)​

Prepare MRI slice GPU resources and upload texture data.

Must be called before a render pass starts. Creates the slice pipeline lazily on first use and uploads the slice texture.

Parameters:

  • rhi : *QRhi ** QRhi pointer.

  • u : *QRhiResourceUpdateBatch ** Resource update batch owned by the caller.

  • slice : *SliceObject ** Pointer to SliceObject; ignored when null.

  • slotIndex : int Slot index (0=axial, 1=coronal, 2=sagittal).

prepareSliceDraw(u, data, slotIndex)​

Write the uniforms of one MRI slice draw into a resource update batch.

Parameters:

  • u : *QRhiResourceUpdateBatch ** Resource update batch, committed before the pass.

  • data : const SceneData & Scene uniforms (MVP, camera position).

  • slotIndex : int Slot index (0=axial, 1=coronal, 2=sagittal).

Returns:

  • int — Uniform buffer offset for this draw, or -1 on failure.

issueSliceDraw(cb, slotIndex, uniformOffset)​

Draw an MRI slice prepared with prepareSliceDraw().

Call inside a pass.

Parameters:

  • cb : *QRhiCommandBuffer ** Command buffer (must be inside a render pass).

  • slotIndex : int Slot index matching the prepareSliceDraw call.

  • uniformOffset : int Offset returned by prepareSliceDraw().

endPass(cb)​

End any render pass (clearing or preserving).

Parameters:

  • cb : *QRhiCommandBuffer ** Command buffer.

Example​

No example of its own: QRhi draw backend owned privately by BrainView; it needs a live GPU device and is driven only through BrainView.

It is exercised by:

src/examples/ex_disp3d_scene/main.cpp
BrainView view; // QRhi widget; nothing is rendered until it is shown
view.setViewCount(2);
const bool twoPanes = view.viewCount() == 2 && view.viewMode() == BrainView::MultiView;
LiveMarker trackerTip;
trackerTip.position = QVector3D(0.0f, 0.08f, 0.04f);
trackerTip.color = Qt::yellow;
view.setLiveMarkers({trackerTip}); // transient, does not move the camera
view.clearLiveMarkers();
view.setViewCount(1);

From ex_disp3d_scene.

Authors of this file​