update Nabla IMGUI backend to use separated immutable sampler with fo…

…nt atlas as 2D array texture, use BDA for requesting texture index. Add comments regarding our base instance indexing as replacement for gl_DrawID and a few more comments + minor changes

include/nbl/ext/ImGui/ImGui.h

@@ -21,10 +21,10 @@ class UI final : public core::IReferenceCounted
 	private:
 		core::smart_refctd_ptr<video::IGPUDescriptorSetLayout> createDescriptorSetLayout();
 		void createPipeline(video::IGPURenderpass* renderpass, video::IGPUPipelineCache* pipelineCache);
-		void createFontTexture(video::IGPUCommandBuffer* cmdBuffer, video::IQueue* queue);
+		void createFontAtlas2DArrayTexture(video::IGPUCommandBuffer* cmdBuffer, video::IQueue* queue);
 		void updateDescriptorSets();
 		void createSystem();
-		void createFontSampler();
+		void createFontAtlasSampler();
 		void createDescriptorPool();
 		void handleMouseEvents(float mousePosX, float mousePosY, size_t mouseEventsCount, ui::SMouseEvent const * mouseEvents) const;
 
@@ -36,7 +36,7 @@ class UI final : public core::IReferenceCounted
 		core::smart_refctd_ptr<video::IDescriptorPool> m_descriptorPool;
 		core::smart_refctd_ptr<video::IGPUDescriptorSet> m_gpuDescriptorSet;
 		core::smart_refctd_ptr<video::IGPUGraphicsPipeline> pipeline;
-		core::smart_refctd_ptr<video::IGPUImageView> m_fontTexture;
+		core::smart_refctd_ptr<video::IGPUImageView> m_fontAtlas2DArrayTexture;
 		core::smart_refctd_ptr<ui::IWindow> m_window;
 		std::vector<core::smart_refctd_ptr<video::IGPUBuffer>> m_mdiBuffers;
 		const uint32_t maxFramesInFlight;

src/nbl/ext/ImGui/ImGui.cpp

@@ -23,15 +23,23 @@ namespace nbl::ext::imgui
 {
 	smart_refctd_ptr<IGPUDescriptorSetLayout> UI::createDescriptorSetLayout()
 	{
-		nbl::video::IGPUDescriptorSetLayout::SBinding bindings[] = 
-		{
+		const IGPUDescriptorSetLayout::SBinding bindings[] = 
+		{ 
 			{
 				.binding = 0u,
-				.type = asset::IDescriptor::E_TYPE::ET_COMBINED_IMAGE_SAMPLER,
+				.type = IDescriptor::E_TYPE::ET_SAMPLED_IMAGE,
+				.createFlags = IGPUDescriptorSetLayout::SBinding::E_CREATE_FLAGS::ECF_NONE,
+				.stageFlags = IShader::ESS_FRAGMENT,
+				.count = 1u,
+				.immutableSamplers = &m_fontSampler
+			},
+			{
+				.binding = 1u,
+				.type = IDescriptor::E_TYPE::ET_SAMPLER,
 				.createFlags = IGPUDescriptorSetLayout::SBinding::E_CREATE_FLAGS::ECF_NONE,
 				.stageFlags = IShader::ESS_FRAGMENT,
-				.count = 1,
-				.samplers = nullptr // TODO: m_fontSampler?
+				.count = 1u,
+				.immutableSamplers = &m_fontSampler
 			}
 		};
 
@@ -45,7 +53,7 @@ namespace nbl::ext::imgui
 		{
 			{
 				.stageFlags = IShader::ESS_VERTEX | IShader::ESS_FRAGMENT,
-				.offset = 0,
+				.offset = 0u,
 				.size = sizeof(PushConstants)
 			}
 		};
@@ -141,7 +149,7 @@ namespace nbl::ext::imgui
 
 			IGPUGraphicsPipeline::SCreationParams params[1];
 			{
-				auto& param = params[0];
+				auto& param = params[0u];
 				param.layout = pipelineLayout.get();
 				param.shaders = specs;
 				param.renderpass = renderpass;
@@ -156,7 +164,7 @@ namespace nbl::ext::imgui
 		}
 	}
 
-	void UI::createFontTexture(video::IGPUCommandBuffer* cmdBuffer, video::IQueue* transfer)
+	void UI::createFontAtlas2DArrayTexture(video::IGPUCommandBuffer* cmdBuffer, video::IQueue* transfer)
 	{
 		// Load Fonts
 		// - If no fonts are loaded, dear imgui will use the default font. You can also load multiple fonts and use ImGui::PushFont()/PopFont() to select them.
@@ -215,7 +223,7 @@ namespace nbl::ext::imgui
 			region->imageSubresource = {};
 			region->imageSubresource.aspectMask = IImage::EAF_COLOR_BIT;
 			region->imageSubresource.layerCount = 1u;
-			region->imageOffset = { 0, 0, 0 };
+			region->imageOffset = { 0u, 0u, 0u };
 			region->imageExtent = { params.extent.width, params.extent.height, 1u };
 		}
 
@@ -233,7 +241,7 @@ namespace nbl::ext::imgui
 			assert(false);
 		}
 
-		image->setObjectDebugName("Nabla IMGUI extension Font Image");
+		image->setObjectDebugName("Nabla IMGUI extension Font Atlas");
 		{
 			IQueue::SSubmitInfo::SCommandBufferInfo cmdInfo = { cmdBuffer };
 			SIntendedSubmitInfo sInfo;
@@ -248,11 +256,11 @@ namespace nbl::ext::imgui
 
 			sInfo.queue = transfer;
 			sInfo.waitSemaphores = {};
-			sInfo.commandBuffers = { &cmdInfo, 1 };
+			sInfo.commandBuffers = { &cmdInfo, 1u };
 			sInfo.scratchSemaphore =
 			{
 				.semaphore = scratchSemaphore.get(),
-				.value = 0,
+				.value = 0u,
 				.stageMask = PIPELINE_STAGE_FLAGS::ALL_TRANSFER_BITS
 			};
 
@@ -312,11 +320,11 @@ namespace nbl::ext::imgui
 		{
 			IGPUImageView::SCreationParams params;
 			params.format = image->getCreationParameters().format;
-			params.viewType = IImageView<IGPUImage>::ET_2D;
+			params.viewType = IImageView<IGPUImage>::ET_2D_ARRAY;
 			params.subresourceRange = regions.subresource;
 			params.image = core::smart_refctd_ptr(image);
 
-			m_fontTexture = m_device->createImageView(std::move(params));
+			m_fontAtlas2DArrayTexture = m_device->createImageView(std::move(params));
 		}
 	}
 
@@ -357,32 +365,26 @@ namespace nbl::ext::imgui
 
 	void UI::updateDescriptorSets()
 	{
-		_NBL_STATIC_INLINE_CONSTEXPR auto NBL_RESOURCES_AMOUNT = 1u;
-
-		IGPUDescriptorSet::SDescriptorInfo info[NBL_RESOURCES_AMOUNT];
-		{
-			auto& font = info[0u];
-			font.desc = m_fontTexture;
-			font.info.image.sampler = m_fontSampler;
-			font.info.image.imageLayout = nbl::asset::IImage::LAYOUT::READ_ONLY_OPTIMAL;
-		}
-
-		IGPUDescriptorSet::SWriteDescriptorSet write[NBL_RESOURCES_AMOUNT];
-		for (auto i = 0u; i < NBL_RESOURCES_AMOUNT; ++i)
-		{
-			auto& w = write[i];
-
-			w.dstSet = m_gpuDescriptorSet.get();
-			w.binding = 0;
-			w.arrayElement = 0;
-			w.count = 1;
-			w.info = info + i;
-		}
+		// texture atlas, note we don't create info & write for the font sampler because ours is immutable and baked into DS layout
+		IGPUDescriptorSet::SDescriptorInfo iInfo = {};
+		iInfo.info.image.imageLayout = IImage::LAYOUT::READ_ONLY_OPTIMAL;
+		iInfo.desc = m_fontAtlas2DArrayTexture;
+
+		const IGPUDescriptorSet::SWriteDescriptorSet writes[] = 
+		{ 
+			{
+				.dstSet = m_gpuDescriptorSet.get(),
+				.binding = 0u,
+				.arrayElement = 0u,
+				.count = 1u,
+				.info = &iInfo
+			} 
+		};
 
-		m_device->updateDescriptorSets(NBL_RESOURCES_AMOUNT, write, 0u, nullptr);
+		m_device->updateDescriptorSets(writes, {});
 	}
 
-	void UI::createFontSampler()
+	void UI::createFontAtlasSampler()
 	{
 		// TODO: Recheck this settings
 		IGPUSampler::SParams params{};
@@ -394,14 +396,15 @@ namespace nbl::ext::imgui
 		params.TextureWrapW = ISampler::ETC_REPEAT;
 
 		m_fontSampler = m_device->createSampler(params);
+		m_fontSampler->setObjectDebugName("Nabla Font Atlas Sampler");
 	}
 
 	void UI::createDescriptorPool()
 	{
 		IDescriptorPool::SCreateInfo createInfo = {};
-		createInfo.maxDescriptorCount[static_cast<uint32_t>(asset::IDescriptor::E_TYPE::ET_COMBINED_IMAGE_SAMPLER)] = 1u;
-		createInfo.maxDescriptorCount[static_cast<uint32_t>(asset::IDescriptor::E_TYPE::ET_STORAGE_BUFFER)] = 1u;
-		createInfo.maxSets = 1;
+		createInfo.maxDescriptorCount[static_cast<uint32_t>(asset::IDescriptor::E_TYPE::ET_SAMPLER)] = 1u;
+		createInfo.maxDescriptorCount[static_cast<uint32_t>(asset::IDescriptor::E_TYPE::ET_SAMPLED_IMAGE)] = 1u;
+		createInfo.maxSets = 1u;
 		createInfo.flags = IDescriptorPool::E_CREATE_FLAGS::ECF_NONE;
 
 		m_descriptorPool = m_device->createDescriptorPool(std::move(createInfo));
@@ -514,11 +517,11 @@ namespace nbl::ext::imgui
 			IMGUI_CHECKVERSION();
 			ImGui::CreateContext();
 
-			createFontSampler();
+			createFontAtlasSampler();
 			createDescriptorPool();
 			createDescriptorSetLayout();
 			createPipeline(renderpass, pipelineCache);
-			createFontTexture(transistentCMD.get(), tQueue);
+			createFontAtlas2DArrayTexture(transistentCMD.get(), tQueue);
 			prepareKeyMapForDesktop();
 			adjustGlobalFontScale();
 			updateDescriptorSets();

src/nbl/ext/ImGui/shaders/common.hlsl

@@ -9,8 +9,8 @@
 	struct PSInput
 	{
 		float4 position : SV_Position;
-		float4 color    : COLOR0;
 		float2 uv : TEXCOORD0;
+		float4 color    : COLOR0;
 		float clip[4] : SV_ClipDistance;
 	};
 

src/nbl/ext/ImGui/shaders/fragment.hlsl

@@ -2,10 +2,20 @@
 
 [[vk::push_constant]] struct PushConstants pc;
 
-[[vk::combinedImageSampler]][[vk::binding(0, 0)]] Texture2D sampleTexture : register(t0);
-[[vk::combinedImageSampler]][[vk::binding(0, 0)]] SamplerState linearSampler : register(s0);
+// separable image samplers, one to handle all textures
+[[vk::binding(0,0)]] Texture2DArray texture;
+[[vk::binding(1,0)]] SamplerState samplerState;
+
+/*
+    we use Indirect Indexed draw call to render whole GUI, note we do a cross 
+    platform trick and use base instance index as replacement for gl_DrawID 
+    to request per object data with BDA
+*/
 
 float4 PSMain(PSInput input, uint drawID : SV_InstanceID) : SV_Target0
 {
-    return input.color * sampleTexture.Sample(linearSampler, input.uv);
+    // BDA for requesting object data
+    const PerObjectData self = vk::RawBufferLoad<PerObjectData>(pc.elementBDA + sizeof(PerObjectData)* drawID);
+
+    return input.color * texture.Sample(samplerState, float32_t3(input.uv, self.texId));
 }

src/nbl/ext/ImGui/shaders/vertex.hlsl

@@ -2,6 +2,12 @@
 
 [[vk::push_constant]] struct PushConstants pc;
 
+/*
+    we use Indirect Indexed draw call to render whole GUI, note we do a cross 
+    platform trick and use base instance index as replacement for gl_DrawID 
+    to request per object data with BDA
+*/
+
 PSInput VSMain(VSInput input, uint drawID : SV_InstanceID)
 {
     PSInput output;
@@ -16,6 +22,7 @@ PSInput VSMain(VSInput input, uint drawID : SV_InstanceID)
     const float2 vMin = self.aabbMin.unpack();
     const float2 vMax = self.aabbMax.unpack();
 
+    // clip planes calculations, axis aligned
     output.clip[0] = output.position.x - vMin.x;
     output.clip[1] = output.position.y - vMin.y;
     output.clip[2] = vMax.x - output.position.x;