qiurui
/
qtdeclarative
mirror of https://github.com/qt/qtdeclarative.git
1
0
Fork 0
Code Issues Packages Projects Releases Wiki Activity

rendernode example: Add support for Metal 

Plus clarify QQuickWindow::begin/endExternalCommands() in combination
with QSGRenderNode in the docs. As the example demonstrates, calling
these functions is not necessary within render() of a render node.

Also fix an issue with resetting the scissor in the renderer after
calling render() of a QSGRenderNode.

Change-Id: If8c2dab38d62aa444266d37901f062a51e767f68
Reviewed-by: Christian Strømme <christian.stromme@qt.io>
This commit is contained in:
Laszlo Agocs 2019-08-16 14:21:15 +02:00
parent ef2715251e
commit 7dcdf3b7ae
11 changed files with 529 additions and 4 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

16
examples/quick/scenegraph/rendernode/customrenderitem.cpp
View File

@ -53,6 +53,7 @@
#include <QSGRendererInterface>
#include "openglrenderer.h"
#include "metalrenderer.h"
#include "d3d12renderer.h"
#include "softwarerenderer.h"
@ -82,6 +83,18 @@ QSGNode *CustomRenderItem::updatePaintNode(QSGNode *node, UpdatePaintNodeData *)
#endif
break;
case QSGRendererInterface::MetalRhi:
#ifdef Q_OS_DARWIN
{
MetalRenderNode *metalNode = new MetalRenderNode(this);
n = metalNode;
metalNode->resourceBuilder()->setWindow(window());
QObject::connect(window(), &QQuickWindow::beforeRendering,
metalNode->resourceBuilder(), &MetalRenderNodeResourceBuilder::build);
}
#endif
break;
case QSGRendererInterface::Direct3D12: // ### Qt 6: remove
#if QT_CONFIG(d3d12)
n = new D3D12RenderNode(this);
@ -102,3 +115,6 @@ QSGNode *CustomRenderItem::updatePaintNode(QSGNode *node, UpdatePaintNodeData *)
return n;
}
//! [2]
// This item does not support being moved between windows. If that is desired,
// itemChange() should be reimplemented as well.

4
examples/quick/scenegraph/rendernode/doc/src/rendernode.qdoc
View File

@ -38,7 +38,9 @@
Metal, Direct 3D, or OpenGL). This example demonstrates implementing a
custom QQuickItem backed by a QSGRenderNode implementation, where the node
renders a triangle directly via the graphics API. The rest of the scene
(background, text, rectangles) are standard Qt Quick items.
(background, text, rectangles) are standard Qt Quick items. The example has
full support for OpenGL and Metal, as well as the software backend of Qt
Quick.
The custom item behaves like any other Qt Quick item, meaning it
participates and stacking and clipping as usual, which is a big difference

1
examples/quick/scenegraph/rendernode/main.qml
View File

@ -146,6 +146,7 @@ Item {
case GraphicsInfo.Direct3D12: apiStr = "Direct3D 12 (direct)"; break;
case GraphicsInfo.Software: apiStr = "Software (QPainter)"; break;
case GraphicsInfo.OpenGLRhi: apiStr = "OpenGL (RHI)"; break;
case GraphicsInfo.MetalRhi: apiStr = "Metal (RHI)"; break;
// the example has no other QSGRenderNode subclasses
default: apiStr = "<UNSUPPORTED>"; break;
}

100
examples/quick/scenegraph/rendernode/metalrenderer.h Normal file
View File

@ -0,0 +1,100 @@
/****************************************************************************
**
** Copyright (C) 2019 The Qt Company Ltd.
** Contact: https://www.qt.io/licensing/
**
** This file is part of the examples of the Qt Toolkit.
**
** $QT_BEGIN_LICENSE:BSD$
** Commercial License Usage
** Licensees holding valid commercial Qt licenses may use this file in
** accordance with the commercial license agreement provided with the
** Software or, alternatively, in accordance with the terms contained in
** a written agreement between you and The Qt Company. For licensing terms
** and conditions see https://www.qt.io/terms-conditions. For further
** information use the contact form at https://www.qt.io/contact-us.
**
** BSD License Usage
** Alternatively, you may use this file under the terms of the BSD license
** as follows:
**
** "Redistribution and use in source and binary forms, with or without
** modification, are permitted provided that the following conditions are
** met:
** * Redistributions of source code must retain the above copyright
** notice, this list of conditions and the following disclaimer.
** * Redistributions in binary form must reproduce the above copyright
** notice, this list of conditions and the following disclaimer in
** the documentation and/or other materials provided with the
** distribution.
** * Neither the name of The Qt Company Ltd nor the names of its
** contributors may be used to endorse or promote products derived
** from this software without specific prior written permission.
**
**
** THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
** "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
** LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
** A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
** OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
** SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
** LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
** DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
** THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
** (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
** OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE."
**
** $QT_END_LICENSE$
**
****************************************************************************/
#ifndef METALRENDERER_H
#define METALRENDERER_H
#include <qsgrendernode.h>
#ifdef Q_OS_DARWIN
QT_BEGIN_NAMESPACE
class QQuickItem;
class QQuickWindow;
QT_END_NAMESPACE
class MetalRenderNodeResourceBuilder : public QObject
{
Q_OBJECT
public:
void setWindow(QQuickWindow *w) { m_window = w; }
public slots:
void build();
private:
QQuickWindow *m_window = nullptr;
};
class MetalRenderNode : public QSGRenderNode
{
public:
MetalRenderNode(QQuickItem *item);
~MetalRenderNode();
void render(const RenderState *state) override;
void releaseResources() override;
StateFlags changedStates() const override;
RenderingFlags flags() const override;
QRectF rect() const override;
MetalRenderNodeResourceBuilder *resourceBuilder() { return &m_resourceBuilder; }
private:
QQuickItem *m_item;
MetalRenderNodeResourceBuilder m_resourceBuilder;
};
#endif // Q_OS_DARWIN
#endif

326
examples/quick/scenegraph/rendernode/metalrenderer.mm Normal file
View File

@ -0,0 +1,326 @@
/****************************************************************************
**
** Copyright (C) 2019 The Qt Company Ltd.
** Contact: https://www.qt.io/licensing/
**
** This file is part of the examples of the Qt Toolkit.
**
** $QT_BEGIN_LICENSE:BSD$
** Commercial License Usage
** Licensees holding valid commercial Qt licenses may use this file in
** accordance with the commercial license agreement provided with the
** Software or, alternatively, in accordance with the terms contained in
** a written agreement between you and The Qt Company. For licensing terms
** and conditions see https://www.qt.io/terms-conditions. For further
** information use the contact form at https://www.qt.io/contact-us.
**
** BSD License Usage
** Alternatively, you may use this file under the terms of the BSD license
** as follows:
**
** "Redistribution and use in source and binary forms, with or without
** modification, are permitted provided that the following conditions are
** met:
** * Redistributions of source code must retain the above copyright
** notice, this list of conditions and the following disclaimer.
** * Redistributions in binary form must reproduce the above copyright
** notice, this list of conditions and the following disclaimer in
** the documentation and/or other materials provided with the
** distribution.
** * Neither the name of The Qt Company Ltd nor the names of its
** contributors may be used to endorse or promote products derived
** from this software without specific prior written permission.
**
**
** THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
** "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
** LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
** A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
** OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
** SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
** LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
** DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
** THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
** (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
** OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE."
**
** $QT_END_LICENSE$
**
****************************************************************************/
#include "metalrenderer.h"
#include <QQuickItem>
#include <QQuickWindow>
#include <Metal/Metal.h>
using FuncAndLib = QPair<id<MTLFunction>, id<MTLLibrary> >;
const int MAX_FRAMES_IN_FLIGHT = 3;
struct {
id<MTLDevice> dev = nil;
QByteArray vsSource;
FuncAndLib vs;
QByteArray fsSource;
FuncAndLib fs;
id<MTLBuffer> vbuf[MAX_FRAMES_IN_FLIGHT];
id<MTLBuffer> ubuf[MAX_FRAMES_IN_FLIGHT];
id<MTLDepthStencilState> stencilEnabledDsState = nil;
id<MTLRenderPipelineState> pipeline = nil;
} g;
static FuncAndLib compileShaderFromSource(const QByteArray &src, const QByteArray &entryPoint)
{
FuncAndLib fl;
NSString *srcstr = [NSString stringWithUTF8String: src.constData()];
MTLCompileOptions *opts = [[MTLCompileOptions alloc] init];
opts.languageVersion = MTLLanguageVersion1_2;
NSError *err = nil;
fl.second = [g.dev newLibraryWithSource: srcstr options: opts error: &err];
[opts release];
// srcstr is autoreleased
if (err) {
const QString msg = QString::fromNSString(err.localizedDescription);
qFatal("%s", qPrintable(msg));
return fl;
}
NSString *name = [NSString stringWithUTF8String: entryPoint.constData()];
fl.first = [fl.second newFunctionWithName: name];
[name release];
return fl;
}
const int VERTEX_SIZE = 6 * sizeof(float);
static float colors[] = {
1.0f, 0.0f, 0.0f,
0.0f, 1.0f, 0.0f,
0.0f, 0.0f, 1.0f
};
void MetalRenderNodeResourceBuilder::build()
{
if (!g.dev) {
QSGRendererInterface *rif = m_window->rendererInterface();
Q_ASSERT(rif->graphicsApi() == QSGRendererInterface::MetalRhi);
g.dev = (id<MTLDevice>) rif->getResource(m_window, QSGRendererInterface::DeviceResource);
Q_ASSERT(g.dev);
}
if (g.vsSource.isEmpty()) {
const QString filename = QLatin1String(":/scenegraph/rendernode/metalshader.vert");
QFile f(filename);
if (!f.open(QIODevice::ReadOnly | QIODevice::Text))
qFatal("Failed to read shader %s", qPrintable(filename));
g.vsSource = f.readAll();
g.vs = compileShaderFromSource(g.vsSource, QByteArrayLiteral("main0"));
}
if (g.fsSource.isEmpty()) {
const QString filename = QLatin1String(":/scenegraph/rendernode/metalshader.frag");
QFile f(filename);
if (!f.open(QIODevice::ReadOnly | QIODevice::Text))
qFatal("Failed to read shader %s", qPrintable(filename));
g.fsSource = f.readAll();
g.fs = compileShaderFromSource(g.fsSource, QByteArrayLiteral("main0"));
}
const int framesInFlight = m_window->graphicsStateInfo()->framesInFlight;
// For simplicity's sake we use shared mode (something like host visible +
// host coherent) for everything.
for (int i = 0; i < framesInFlight; ++i) {
// Have multiple versions for vertex too since we'll just memcpy new
// vertices based on item width and height on every render(). This could
// be optimized further however.
if (!g.vbuf[i]) {
g.vbuf[i] = [g.dev newBufferWithLength: VERTEX_SIZE + sizeof(colors) options: MTLResourceStorageModeShared];
char *p = (char *) [g.vbuf[i] contents];
memcpy(p + VERTEX_SIZE, colors, sizeof(colors));
}
if (!g.ubuf[i])
g.ubuf[i] = [g.dev newBufferWithLength: 256 options: MTLResourceStorageModeShared];
}
if (!g.stencilEnabledDsState) {
MTLDepthStencilDescriptor *dsDesc = [[MTLDepthStencilDescriptor alloc] init];
dsDesc.frontFaceStencil = [[MTLStencilDescriptor alloc] init];
dsDesc.frontFaceStencil.stencilFailureOperation = MTLStencilOperationKeep;
dsDesc.frontFaceStencil.depthFailureOperation = MTLStencilOperationKeep;
dsDesc.frontFaceStencil.depthStencilPassOperation = MTLStencilOperationKeep;
dsDesc.frontFaceStencil.stencilCompareFunction = MTLCompareFunctionEqual;
dsDesc.frontFaceStencil.readMask = 0xFF;
dsDesc.frontFaceStencil.writeMask = 0xFF;
dsDesc.backFaceStencil = [[MTLStencilDescriptor alloc] init];
dsDesc.backFaceStencil.stencilFailureOperation = MTLStencilOperationKeep;
dsDesc.backFaceStencil.depthFailureOperation = MTLStencilOperationKeep;
dsDesc.backFaceStencil.depthStencilPassOperation = MTLStencilOperationKeep;
dsDesc.backFaceStencil.stencilCompareFunction = MTLCompareFunctionEqual;
dsDesc.backFaceStencil.readMask = 0xFF;
dsDesc.backFaceStencil.writeMask = 0xFF;
g.stencilEnabledDsState = [g.dev newDepthStencilStateWithDescriptor: dsDesc];
[dsDesc release];
}
if (!g.pipeline) {
MTLVertexDescriptor *inputLayout = [MTLVertexDescriptor vertexDescriptor];
inputLayout.attributes[0].format = MTLVertexFormatFloat2;
inputLayout.attributes[0].offset = 0;
inputLayout.attributes[0].bufferIndex = 1; // ubuf is 0, vbuf is 1 and 2
inputLayout.attributes[1].format = MTLVertexFormatFloat3;
inputLayout.attributes[1].offset = 0;
inputLayout.attributes[1].bufferIndex = 2;
inputLayout.layouts[1].stride = 2 * sizeof(float);
inputLayout.layouts[2].stride = 3 * sizeof(float);
MTLRenderPipelineDescriptor *rpDesc = [[MTLRenderPipelineDescriptor alloc] init];
rpDesc.vertexDescriptor = inputLayout;
rpDesc.vertexFunction = g.vs.first;
rpDesc.fragmentFunction = g.fs.first;
rpDesc.colorAttachments[0].pixelFormat = MTLPixelFormatBGRA8Unorm;
rpDesc.colorAttachments[0].blendingEnabled = true;
rpDesc.colorAttachments[0].sourceRGBBlendFactor = MTLBlendFactorOne;
rpDesc.colorAttachments[0].sourceAlphaBlendFactor = MTLBlendFactorOne;
rpDesc.colorAttachments[0].destinationRGBBlendFactor = MTLBlendFactorOneMinusSourceAlpha;
rpDesc.colorAttachments[0].destinationAlphaBlendFactor = MTLBlendFactorOneMinusSourceAlpha;
if (g.dev.depth24Stencil8PixelFormatSupported) {
rpDesc.depthAttachmentPixelFormat = MTLPixelFormatDepth24Unorm_Stencil8;
rpDesc.stencilAttachmentPixelFormat = MTLPixelFormatDepth24Unorm_Stencil8;
} else {
rpDesc.depthAttachmentPixelFormat = MTLPixelFormatDepth32Float_Stencil8;
rpDesc.stencilAttachmentPixelFormat = MTLPixelFormatDepth32Float_Stencil8;
}
NSError *err = nil;
g.pipeline = [g.dev newRenderPipelineStateWithDescriptor: rpDesc error: &err];
if (!g.pipeline) {
const QString msg = QString::fromNSString(err.localizedDescription);
qFatal("Failed to create render pipeline state: %s", qPrintable(msg));
}
[rpDesc release];
}
}
MetalRenderNode::MetalRenderNode(QQuickItem *item)
: m_item(item)
{
g.vs.first = g.fs.first = nil;
g.vs.second = g.fs.second = nil;
for (int i = 0; i < MAX_FRAMES_IN_FLIGHT; ++i) {
g.vbuf[i] = nil;
g.ubuf[i] = nil;
}
}
MetalRenderNode::~MetalRenderNode()
{
releaseResources();
}
void MetalRenderNode::releaseResources()
{
[g.stencilEnabledDsState release];
g.stencilEnabledDsState = nil;
[g.pipeline release];
g.pipeline = nil;
[g.vs.first release];
[g.vs.second release];
[g.fs.first release];
[g.fs.second release];
g.vs.first = g.fs.first = nil;
g.vs.second = g.fs.second = nil;
for (int i = 0; i < MAX_FRAMES_IN_FLIGHT; ++i) {
[g.vbuf[i] release];
g.vbuf[i] = nil;
[g.ubuf[i] release];
g.ubuf[i] = nil;
}
}
void MetalRenderNode::render(const RenderState *state)
{
QQuickWindow *window = m_item->window();
const QQuickWindow::GraphicsStateInfo *stateInfo = window->graphicsStateInfo();
id<MTLBuffer> vbuf = g.vbuf[stateInfo->currentFrameSlot];
id<MTLBuffer> ubuf = g.ubuf[stateInfo->currentFrameSlot];
QPointF p0(m_item->width() - 1, m_item->height() - 1);
QPointF p1(0, 0);
QPointF p2(0, m_item->height() - 1);
float vertices[6] = { float(p0.x()), float(p0.y()),
float(p1.x()), float(p1.y()),
float(p2.x()), float(p2.y()) };
char *p = (char *) [vbuf contents];
memcpy(p, vertices, VERTEX_SIZE);
const QMatrix4x4 mvp = *state->projectionMatrix() * *matrix();
const float opacity = inheritedOpacity();
p = (char *) [ubuf contents];
memcpy(p, mvp.constData(), 64);
memcpy(p + 64, &opacity, 4);
QSGRendererInterface *rif = window->rendererInterface();
id<MTLRenderCommandEncoder> encoder = (id<MTLRenderCommandEncoder>) rif->getResource(
window, QSGRendererInterface::CommandEncoderResource);
Q_ASSERT(encoder);
[encoder setVertexBuffer: vbuf offset: 0 atIndex: 1];
[encoder setVertexBuffer: vbuf offset: VERTEX_SIZE atIndex: 2];
[encoder setVertexBuffer: ubuf offset: 0 atIndex: 0];
[encoder setFragmentBuffer: ubuf offset: 0 atIndex: 0];
// Clip support.
if (state->scissorEnabled()) {
const QRect r = state->scissorRect(); // bottom-up
MTLScissorRect s;
s.x = r.x();
s.y = (window->height() * window->effectiveDevicePixelRatio()) - (r.y() + r.height());
s.width = r.width();
s.height = r.height();
[encoder setScissorRect: s];
}
if (state->stencilEnabled()) {
[encoder setDepthStencilState: g.stencilEnabledDsState];
[encoder setStencilReferenceValue: state->stencilValue()];
}
[encoder setRenderPipelineState: g.pipeline];
[encoder drawPrimitives: MTLPrimitiveTypeTriangle vertexStart: 0 vertexCount: 3 instanceCount: 1 baseInstance: 0];
}
QSGRenderNode::StateFlags MetalRenderNode::changedStates() const
{
return BlendState | ScissorState | StencilState;
}
QSGRenderNode::RenderingFlags MetalRenderNode::flags() const
{
return BoundedRectRendering | DepthAwareRendering;
}
QRectF MetalRenderNode::rect() const
{
return QRect(0, 0, m_item->width(), m_item->height());
}

28
examples/quick/scenegraph/rendernode/metalshader.frag Normal file
View File

@ -0,0 +1,28 @@
#include <metal_stdlib>
#include <simd/simd.h>
using namespace metal;
struct buf
{
float4x4 matrix;
float opacity;
};
struct main0_out
{
float4 fragColor [[color(0)]];
};
struct main0_in
{
float4 v_color [[user(locn0)]];
};
fragment main0_out main0(main0_in in [[stage_in]], constant buf& ubuf [[buffer(0)]])
{
main0_out out = {};
out.fragColor = in.v_color * ubuf.opacity;
return out;
}

31
examples/quick/scenegraph/rendernode/metalshader.vert Normal file
View File

@ -0,0 +1,31 @@
#include <metal_stdlib>
#include <simd/simd.h>
using namespace metal;
struct buf
{
float4x4 matrix;
float opacity;
};
struct main0_out
{
float4 v_color [[user(locn0)]];
float4 gl_Position [[position]];
};
struct main0_in
{
float4 pos [[attribute(0)]];
float4 color [[attribute(1)]];
};
vertex main0_out main0(main0_in in [[stage_in]], constant buf& ubuf [[buffer(0)]])
{
main0_out out = {};
out.v_color = in.color;
out.gl_Position = ubuf.matrix * in.pos;
return out;
}

6
examples/quick/scenegraph/rendernode/rendernode.pro
View File

@ -22,3 +22,9 @@ qtConfig(d3d12) {
SOURCES += d3d12renderer.cpp
LIBS += -ld3d12
}
macos {
HEADERS += metalrenderer.h
SOURCES += metalrenderer.mm
LIBS += -framework Metal -framework AppKit
}

2
examples/quick/scenegraph/rendernode/rendernode.qrc
View File

@ -3,5 +3,7 @@
<file>main.qml</file>
<file>shader_vert.cso</file>
<file>shader_frag.cso</file>
<file>metalshader.vert</file>
<file>metalshader.frag</file>
</qresource>
</RCC>

10
src/quick/items/qquickwindow.cpp
View File

@ -4666,6 +4666,11 @@ const QQuickWindow::GraphicsStateInfo *QQuickWindow::graphicsStateInfo()
beginExternalCommands() and endExternalCommands() together provide a
replacement for resetOpenGLState().
Calling this function and endExternalCommands() is not necessary within the
\l{QSGRenderNode::render()}{render()} implementation of a QSGRenderNode
because the scene graph performs the necessary steps implicitly for render
nodes.
\note This function has no effect when the scene graph is using OpenGL
directly and the RHI graphics abstraction layer is not in use. Refer to
resetOpenGLState() in that case.
@ -4704,6 +4709,11 @@ void QQuickWindow::beginExternalCommands()
beginExternalCommands() and endExternalCommands() together provide a
replacement for resetOpenGLState().
Calling this function and beginExternalCommands() is not necessary within the
\l{QSGRenderNode::render()}{render()} implementation of a QSGRenderNode
because the scene graph performs the necessary steps implicitly for render
nodes.
\note This function has no effect when the scene graph is using OpenGL
directly and the RHI graphics abstraction layer is not in use. Refer to
resetOpenGLState() in that case.

9
src/quick/scenegraph/coreapi/qsgbatchrenderer.cpp
View File

@ -4563,11 +4563,14 @@ void Renderer::renderRhiRenderNode(const Batch *batch) // split prepare-render (
rd->m_matrix = nullptr;
rd->m_clip_list = nullptr;
if (changes & QSGRenderNode::ViewportState)
if ((changes & QSGRenderNode::ViewportState)
|| (changes & QSGRenderNode::ScissorState))
{
// Reset both flags if either is reported as changed, since with the rhi
// it could be setViewport() that will record the resetting of the scissor.
m_pstate.viewportSet = false;
if (changes & QSGRenderNode::ScissorState)
m_pstate.scissorSet = false;
}
// Do not bother with RenderTargetState. Where applicable, endExternal()
// ensures the correct target is rebound. For others (like Vulkan) it makes