* Fix rare crash when switching renderers

* Abandon QPainter in hardware renderers in favour of OpenGL
* Disable VSync in the application globally

src/qt/qt_hardwarerenderer.cpp

@@ -16,10 +16,18 @@ void HardwareRenderer::initializeGL()
 {
     m_context->makeCurrent(this);
     initializeOpenGLFunctions();
+    m_texture = new QOpenGLTexture(image);
+    m_blt = new QOpenGLTextureBlitter;
+    m_blt->setRedBlueSwizzle(true);
+    m_blt->create();
 }
 
 void HardwareRenderer::paintGL() {
-    onPaint(this);
+    m_context->makeCurrent(this);
+    m_blt->bind();
+    QMatrix4x4 target = QOpenGLTextureBlitter::targetTransform(QRect(0, 0, 2048, 2048), source);
+    m_blt->blit(m_texture->textureId(), target, QOpenGLTextureBlitter::Origin::OriginTopLeft);
+    m_blt->release();
 }
 
 void HardwareRenderer::setRenderType(RenderType type) {
@@ -37,7 +45,11 @@ void HardwareRenderer::setRenderType(RenderType type) {
 }
 
 void HardwareRenderer::onBlit(const std::unique_ptr<uint8_t>* img, int x, int y, int w, int h, std::atomic_flag* in_use) {
-    memcpy(image.bits(), img->get(), 2048 * 2048 * 4);
+    auto tval = this;
+    void* nuldata = 0;
+    if (memcmp(&tval, &nuldata, sizeof(void*)) == 0) return;
+    m_context->makeCurrent(this);
+    m_texture->setData(QOpenGLTexture::PixelFormat::RGBA, QOpenGLTexture::PixelType::UInt8, (const void*)img->get());
     in_use->clear();
     source.setRect(x, y, w, h);
     update();

src/qt/qt_hardwarerenderer.hpp

@@ -3,6 +3,10 @@
 #include <QOpenGLFunctions>
 #include <QOpenGLWidget>
 #include <QOpenGLWindow>
+#include <QOpenGLTexture>
+#include <QOpenGLShader>
+#include <QOpenGLShaderProgram>
+#include <QOpenGLTextureBlitter>
 #include <QPainter>
 #include <QEvent>
 #include <QKeyEvent>
@@ -25,6 +29,9 @@ private:
     bool wayland = false;
     QWidget* parentWidget{nullptr};
     QOpenGLContext* m_context;
+    QOpenGLTexture* m_texture;
+    QOpenGLShaderProgram* m_prog;
+    QOpenGLTextureBlitter* m_blt;
 public:
     void resizeGL(int w, int h) override;
     void initializeGL() override;
@@ -41,7 +48,8 @@ public:
     }
     ~HardwareRenderer()
     {
-        makeCurrent();
+        m_context->makeCurrent(this);
+        if (m_blt) m_blt->destroy();
     }
 
     enum class RenderType {

src/qt/qt_main.cpp

@@ -1,4 +1,5 @@
 #include <QApplication>
+#include <QSurfaceFormat>
 #include <QDebug>
 #include <QElapsedTimer>
 #include <QThread>
@@ -94,6 +95,9 @@ main_thread_fn()
 
 int main(int argc, char* argv[]) {
     QApplication app(argc, argv);
+    QSurfaceFormat fmt = QSurfaceFormat::defaultFormat();
+    fmt.setSwapInterval(0);
+    QSurfaceFormat::setDefaultFormat(fmt);
     app.setStyle(new StyleOverride());
 #ifdef __APPLE__
     CocoaEventFilter cocoafilter;

src/qt/qt_rendererstack.cpp

@@ -203,6 +203,7 @@ void RendererStack::switchRenderer(Renderer renderer) {
     current->setFocusProxy(this);
     addWidget(current.get());
 
+    this->setStyleSheet("background-color: black");
     for (auto& in_use : buffers_in_use)
         in_use.clear();
 

src/qt/qt_softwarerenderer.cpp

@@ -8,6 +8,9 @@ void SoftwareRenderer::paintEvent(QPaintEvent *event) {
 }
 
 void SoftwareRenderer::onBlit(const std::unique_ptr<uint8_t>* img, int x, int y, int w, int h, std::atomic_flag* in_use) {
+    auto tval = this;
+    void* nuldata = 0;
+    if (memcmp(&tval, &nuldata, sizeof(void*)) == 0) return;
     memcpy(image.bits(), img->get(), 2048 * 2048 * 4);
     in_use->clear();
     source.setRect(x, y, w, h);