Correction. I do not why. But my proposal no more works. But I found another way that seems to work. In fact the QDiffuseSpecularMaterial that we are supposed to use (other materials are deprecated), disable the depth buffer. So, this is a working code to force the enable (create a new effect does not work):

Qt3DRender::QEffect *effect = material->effect(); if (effect) { for (Qt3DRender::QTechnique* currentTechnique : effect->techniques()) { for (Qt3DRender::QRenderPass * currentPass : currentTechnique->renderPasses()) { for (Qt3DRender::QRenderState * currentState : currentPass->renderStates()) { if (dynamic_cast<Qt3DRender::QNoDepthMask *>(currentState)) { currentPass->removeRenderState(currentState); Qt3DRender::QDepthTest* depthTest = new Qt3DRender::QDepthTest; depthTest ->setDepthFunction(Qt3DRender::QDepthTest::Less); currentPass->addRenderState(depthTest); break; } } } } }

Warning: if you have fully transparent (alpha = 0) objects, the test fails. So the objects behind the invisible one are not displayed.