rhi: vulkan: Fix multisample resolve with multiview

Task-number: QTBUG-114790
Change-Id: I3afccc3f7ae2d05aa9aa0e0943aeadc080016f0e
Reviewed-by: Andy Nichols <andy.nichols@qt.io>

src/gui/rhi/qrhi.cpp

@@ -2284,16 +2284,40 @@ QRhiColorAttachment::QRhiColorAttachment(QRhiRenderBuffer *renderBuffer)
     \nullptr if there is none.
 
     Setting a non-null resolve texture is applicable when the attachment
-    references a multisample, color renderbuffer. (i.e., renderBuffer() is set)
+    references a multisample texture or renderbuffer. The QRhiTexture in the
-    The QRhiTexture in the resolveTexture() is then a regular, 2D,
+    resolveTexture() is then a non-multisample 2D texture (or texture array)
-    non-multisample texture with the same size (but a sample count of 1). The
+    with the same size (but a sample count of 1). The multisample content is
-    multisample content is automatically resolved into this texture at the end
+    automatically resolved into this texture at the end of each render pass.
-    of each render pass.
  */
 
 /*!
     \fn void QRhiColorAttachment::setResolveTexture(QRhiTexture *tex)
+
     Sets the resolve texture \a tex.
+
+    \a tex is expected to be a 2D texture or a 2D texture array. In either
+    case, resolving targets a single mip level of a single layer (array
+    element) of \a tex. The mip level and array layer are specified by
+    resolveLevel() and resolveLayer().
+
+    An exception is \l{setMultiViewCount()}{multiview}: when the color
+    attachment is associated with a texture array and multiview is enabled, the
+    resolve texture must also be a texture array with sufficient elements for
+    all views. In this case all elements that correspond to views are resolved
+    automatically; the behavior is similar to the following pseudo-code:
+    \badcode
+        for (i = 0; i < multiViewCount(); ++i)
+            resolve texture's layer() + i into resolveTexture's resolveLayer() + i
+    \endcode
+
+    Setting a non-multisample texture to resolve a multisample texture or
+    renderbuffer automatically at the end of the render pass is often
+    preferable to working with multisample textures (and not setting a resolve
+    texture), because it avoids the need for writing dedicated fragment shaders
+    that work exclusively with multisample textures (\c sampler2DMS, \c
+    texelFetch, etc.), and rather allows using the same shader as one would if
+    the attachment's texture was not multisampled to begin with. This comes at
+    the expense of an additional resource (the non-multisample \a tex).
  */
 
 /*!

src/gui/rhi/qrhivulkan.cpp

@@ -6723,6 +6723,7 @@ bool QVkTextureRenderTarget::create()
 
     QRHI_RES_RHI(QRhiVulkan);
     QVarLengthArray<VkImageView, 8> views;
+    uint32_t multiViewCount = 0;
 
     d.colorAttCount = 0;
     int attIndex = 0;
@@ -6735,6 +6736,8 @@ bool QVkTextureRenderTarget::create()
             Q_ASSERT(texD->flags().testFlag(QRhiTexture::RenderTarget));
             const bool is1D = texD->flags().testFlag(QRhiTexture::OneDimensional);
             const bool isMultiView = it->multiViewCount() >= 2;
+            if (isMultiView && multiViewCount == 0)
+                multiViewCount = uint32_t(it->multiViewCount());
             VkImageViewCreateInfo viewInfo = {};
             viewInfo.sType = VK_STRUCTURE_TYPE_IMAGE_VIEW_CREATE_INFO;
             viewInfo.image = texD->image;
@@ -6795,6 +6798,7 @@ bool QVkTextureRenderTarget::create()
 
     d.resolveAttCount = 0;
     attIndex = 0;
+    Q_ASSERT(multiViewCount == 0 || multiViewCount >= 2);
     for (auto it = m_desc.cbeginColorAttachments(), itEnd = m_desc.cendColorAttachments(); it != itEnd; ++it, ++attIndex) {
         if (it->resolveTexture()) {
             QVkTexture *resTexD = QRHI_RES(QVkTexture, it->resolveTexture());
@@ -6804,7 +6808,8 @@ bool QVkTextureRenderTarget::create()
             VkImageViewCreateInfo viewInfo = {};
             viewInfo.sType = VK_STRUCTURE_TYPE_IMAGE_VIEW_CREATE_INFO;
             viewInfo.image = resTexD->image;
-            viewInfo.viewType = VK_IMAGE_VIEW_TYPE_2D;
+            viewInfo.viewType = multiViewCount ? VK_IMAGE_VIEW_TYPE_2D_ARRAY
+                                               : VK_IMAGE_VIEW_TYPE_2D;
             viewInfo.format = resTexD->vkformat;
             viewInfo.components.r = VK_COMPONENT_SWIZZLE_R;
             viewInfo.components.g = VK_COMPONENT_SWIZZLE_G;
@@ -6814,7 +6819,7 @@ bool QVkTextureRenderTarget::create()
             viewInfo.subresourceRange.baseMipLevel = uint32_t(it->resolveLevel());
             viewInfo.subresourceRange.levelCount = 1;
             viewInfo.subresourceRange.baseArrayLayer = uint32_t(it->resolveLayer());
-            viewInfo.subresourceRange.layerCount = 1;
+            viewInfo.subresourceRange.layerCount = qMax(1u, multiViewCount);
             VkResult err = rhiD->df->vkCreateImageView(rhiD->dev, &viewInfo, nullptr, &resrtv[attIndex]);
             if (err != VK_SUCCESS) {
                 qWarning("Failed to create render target resolve image view: %d", err);