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OpenGL Pros and Cons for Batching Sprites

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I thought sprite batches were the way to go for the last 3 years, but the more I use my sprite batch system, the more I wonder if it's actually helping? I understand the benefits: fewer texture swaps, shader swaps and draw calls overall.

 

The way I use my sprite batch class is to accomplish what I described above. I have a Sprite class which I create instances of, and add them to my SpriteBatch instance which also has a reference to a texture atlas. I can setup each sprite's blitting data, transform them, etc. and the Sprite Batch will keep track of every sprite's vertices in a single array.

 

Life is good, isn't it? Then, I started analyzing the cons I've found using them:

-Most sprites aren't using the same texture all that frequently unless you're using a tile map, but tile maps can be handled as a special-case anyway. Outside of that, it's very rare to have the same sprite show up multiple times onscreen.

-Batching requires all sprites to software-transform the vertices they own in the vertex array in OpenGL ES 2.0 --very common right now for mobile games

-If you wanted to make a sprite invisible because you didn't want to render it at that time, you couldn't just simply not render it. You'd have to give that sprite's vertices an alpha value of zero so they're completely transparent. This is a blending performance killer on mobile devices

-Frustum culling is inefficient. If you use a sprite batch for a large area that has many of the same sprite, say, the same enemy, you'll be able to draw them all at once easily, but usually only a couple of them, if any, are onscreen at a time

-Color data is needed per vertex to apply a color overlay to a sprite instead of a single uniform because its vertices are batched with the rest

-Any time you want to draw a sprite, you need a sprite batch. This is a pain if you're making an RPG with 4 main characters where they each have their own batches. Each character needs its own sprite batch for their sprite even though they're the only instance that'll ever need it at a time

-Storing a sprite in multiple lists are a pain as well. I'm writing a 2D engine where each Sprite is a scene object with its own transform matrix. Not only does it have to be included in the scene's object dictionary (STL map), but now its corresponding sprite batch needs to keep a pointer to it in its own list. This is problematic because if the Sprite is released from memory, I now need to make sure both the batch and scene know it.

 

Just my thoughts

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I'm currently having similar thoughts about implementing a sprite batcher, and your post even got me thinking about some problems I hadn't thought of before. As such, remember that all follows are answers from the top of my head that may or may not work as I have yet to implement this myself.

 


-Batching requires all sprites to software-transform the vertices they own in the vertex array in OpenGL ES 2.0 --very common right now for mobile games

If done at load time this shouldn't be a problem, no?

I'm assuming you only geometry-batch static sprites.

 


-If you wanted to make a sprite invisible because you didn't want to render it at that time, you couldn't just simply not render it. You'd have to give that sprite's vertices an alpha value of zero so they're completely transparent. This is a blending performance killer on mobile devices

Maybe increasing draw calls to only draw the visible indices would help. Once an object is invisible for more than a number of frames or more than X objects are hidden, rebuild the indices to only contain the visible instances. Having some pools of indices would help limiting the work done when rebuilding the indices.

 


-Frustum culling is inefficient. If you use a sprite batch for a large area that has many of the same sprite, say, the same enemy, you'll be able to draw them all at once easily, but usually only a couple of them, if any, are onscreen at a time

Try force-splitting the batches in chunks of a certain area. Say, a chunk only covers a 512x512 pixel area at most (only count the sprites' centers, not their dimensions).This will make even less sprites fit a batch, but maybe it's still worh it... This may however add to the difficulty of properly sorting the faces to render front-to-back (if you need that).

 


-Any time you want to draw a sprite, you need a sprite batch. This is a pain if you're making an RPG with 4 main characters where they each have their own batches. Each character needs its own sprite batch for their sprite even though they're the only instance that'll ever need it at a time

Assuming your engine is aware of the difference between static sprites and dynamic sprites, the performance loss of putting your character sprites through the system should be negligible.

The interface you use to feed the sprites to your engine should also be simple enough that the user will barely notice that the sprites will get batched before rendering.

 


-Storing a sprite in multiple lists are a pain as well. I'm writing a 2D engine where each Sprite is a scene object with its own transform matrix. Not only does it have to be included in the scene's object dictionary (STL map), but now its corresponding sprite batch needs to keep a pointer to it in its own list. This is problematic because if the Sprite is released from memory, I now need to make sure both the batch and scene know it.

There probably are many solutions to this problem, Maybe your Sprite class should be the one notifying the batcher of its existence and destruction in it's ctor and dtor respectively? Or maybe you could use something like boost::signals to expose some events on the sprite, something like sprite->getSignal_onDestroy().connect(...). Or implement a sprite::addListener( ISpriteListenet* ).

 

 

The solutions also depend on the type of scene; how many static sprites are there, how many dynamic ones, is instancing used etc.

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-Most sprites aren't using the same texture all that frequently unless you're using a tile map, but tile maps can be handled as a special-case anyway. Outside of that, it's very rare to have the same sprite show up multiple times onscreen.

If performance is critical and your sprite usage is very dynamic (i.e. you can't create a texture atlas offline) you need to create a system that would take the textures being used, and batch them into a single texture atlas.
It's not easy, but it isn't that hard either.

If you're developing for DX11/GL3; then you can use texture arrays instead which is much simpler and solves the issue.
 

-Batching requires all sprites to software-transform the vertices they own in the vertex array in OpenGL ES 2.0 --very common right now for mobile games

And this is a problem because...?
 

-If you wanted to make a sprite invisible because you didn't want to render it at that time, you couldn't just simply not render it. You'd have to give that sprite's vertices an alpha value of zero so they're completely transparent. This is a blending performance killer on mobile devices

If you're manipulating the sprite vertices to change the alpha value, then:
  • You can just not include the vertices when regenerating the vertex buffer.
  • If you're overwriting just a subregion, then a more clever approach than setting alpha to 0 is to move the vertices out of the viewport region. All vertices will be culled and pixel processing power won't be wasted on them; only for the vertices.

-Frustum culling is inefficient. If you use a sprite batch for a large area that has many of the same sprite, say, the same enemy, you'll be able to draw them all at once easily, but usually only a couple of them, if any, are onscreen at a time

Yes. This is a trade off. Partition your batch into smaller batches, but not small enough to become one batch per sprite.
Additionally, if your API supports instancing (or you're passing each sprite position through a constant register) then culling is still possible. If you can draw up to 80 sprites but only 2 are visible, then divide the number of vertices by 40.
The fact that your vertex buffer can hold 80 * 4 vertices (assuming 4 vertices per sprite) doesn't mean you can't pass less to the draw call.
If you're using instancing, just pass a lower instance count.

-Any time you want to draw a sprite, you need a sprite batch. This is a pain if you're making an RPG with 4 main characters where they each have their own batches. Each character needs its own sprite batch for their sprite even though they're the only instance that'll ever need it at a time

I prefer a more generic batching system that accepts "any" kind of sprite and batches it together (generating the atlas on the fly) and then reuse. However this only works well if the sprites can be grouped by shared properties that last long enough.

Indeed, batching isn't a silver bullet, it does come with trade offs or problems. But generally speaking does it's job in improving performance (with some exceptions, when all the content is too dynamic), and some of the problems you're mentioning are easily solvable.

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I only transform the vertices if something has changed since the last frame, which is nice if it's static. A downside to consider, however, is that each sprite requires as second set of position, rotation and scale data which can be bloating, and if even just one thing changes, you'd have to re-multiply the translation, rotation and scale matrices together to get the new transform matrix, then multiply pre-multiply its parent matrix by that if it's attached to another scene element, and finally multiply each vertex by that matrix. It can be memory-intensive too as my old sprite module's size was around 1500 bytes per sprite instance! It had all kinds of features though, but imagine using thousands of those instances as static sprites in a tile map. That's megabytes of just metadata lol... (That's not counting the actual vertex/index data in the batch).

 

I've thought about index pools as alpha blending combined with limited filtrate on mobile devices are huge restrictions. It'd just be bad to have to hide a 256x256 sprite with alpha blending from all the texture look-ups alone.

 

Btw, as far as sorting goes, I use the depth buffer along with 3D coordinates in my vertex format. I thought about trimming the vertex struct down to 2D positions with a "depth" value per sprite, but that won't work with batching since OpenGL ES 2.0 doesn't support UBOs like desktop OpenGL 3.3 lol. Due to this, color and depth information per sprite is copied into each of the sprite's vertices until we start seeing OpenGL ES 3.0 hardware.

 


Vincent_M, on 25 Aug 2013 - 5:30 PM, said:

-Any time you want to draw a sprite, you need a sprite batch. This is a pain if you're making an RPG with 4 main characters where they each have their own batches. Each character needs its own sprite batch for their sprite even though they're the only instance that'll ever need it at a time
Assuming your engine is aware of the difference between static sprites and dynamic sprites, the performance loss of putting your character sprites through the system should be negligible.
The interface you use to feed the sprites to your engine should also be simple enough that the user will barely notice that the sprites will get batched before rendering.

 

By static, do you mean moving/non-moving? My sprite batch just contains a single STL vector of vertices for all sprites attached to it. Having only a single sprite in a sprite batch wouldn't be slower than drawing sprites individually, but it's more setup code as you'd have to load the texture, allocate the sprite batch, link the texture to the sprite batch, allocate a sprite, link it to the sprite batch, setup sprite blitting params, then transform/update animations as necessary.

 

Then again, my SpriteBatch class does contain a list of metadata for sprite sheet animations too. You'd define the dimensions of the animation frame, how many frames, etc in a SpriteAnimation object, then link that to your SpriteBatch instance that's keeping reference to the sprite sheet texture. Then, the sprite instance just needs to use SetAnimation(), frame trimming, playback state, playback framerate (all optional), etc.

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@Matias: I'm trying to add onto my reply above since your post came in after my reply, but it doesn't seem to let me, so I apologize in advance for the double post. Here's are my replies to your points:

 

-I've seen some good things in OpenGL 3.3, but my main target is mobile (yep, I'm on  the mobile bandwagon...). I'm excited for OpenGL ES 3.0 since the specification does appear to support batching and MRTs for deferred rendering, but it looks like it could be a while before we start seeing devices that completely support the spec.

 

-Software rendering is probably a benefit for static sprites as you just transform them once, and update them whenever something changes in the future instead of every frame in a vertex shader. However, software transformation is kind of intense when something actually does change because there's 3, possibly 4 matrix4x4 multiplications and 4 matrix4x4 * vector3 operations. That's 48 to 64 dot products for the matrix multiplication and 12 more dot products to transform the vertices.

 

-As far as frustum culling is concerned, I may stop using my current Sprite class for tile maps and create a simpler sprite class that treats the sprites as static and generates sprite batches based on a quadtree. If I want anything dynamic, I'll treat them as actual sprites with full functionality that character sprites would have.

 

-So, if I move the vertices out of the viewport, the GPU won't attempt to draw them? I'm still sending the data to the GPU, but if it's outside the viewport upon final transformation in the vertex shader, the pixel shader won't be processed? If I understood that correctly, then I feel better about my fill rate concerns. I'm still sending unnecessary data to the GPU, but then again 3D games are sending way more vertex data to GPU with frustum culling than you'd encounter in an entire 2D scene, generally. I would think anyway.

 

-I've thought about writing an atlas generator, but it was meant to be a tool to generate them offline and produce meta data to tell my SpriteBatch class the coordinates of the sprites and animation frames held in the atlas. On-the-fly generation seems as if it could produce long load times as you'd be loading many separate image files at once instead of one larger one, and possibly generating sprite definition data on-the-spot.

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Most of thee worries involve negligible amounts of data and processing: for example, adding a colour to every one of hundreds and hundreds of sprites amounts to 1 (index) to 8 (16-bit RGBA) hundreds and hundreds of bytes per frame. Are there technical reasons to use many batches instead of putting all compatible sprites in the same batch? Singleton or almost singleton entities like the "4 main characters" can have reserved places in a shared vertex buffer rather than their separate batches.

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For batching 3d meshes I have a system which allows me to:

 

- batch "batches" (store only the list pointer)

- batch single meshes (store the data in a local list)

 

I use the mesh batches for blocks which don't change so often. So in this case efficient culling comes at price of drawing out-of-frustum objects. 

Instead of copying data (except for the single mesh case) I only add a batch list to a list of batches. Before drawing I upload the data to a buffer object (could be constant buffer or vertex buffer). So this way I can have one draw call per mesh type regardless how the meshes are batched. This can be implemented with sprites too. Of course it involves copying data around which may be less efficient with mobile devices.

 

Cheers!

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Most of thee worries involve negligible amounts of data and processing: for example, adding a colour to every one of hundreds and hundreds of sprites amounts to 1 (index) to 8 (16-bit RGBA) hundreds and hundreds of bytes per frame. Are there technical reasons to use many batches instead of putting all compatible sprites in the same batch? Singleton or almost singleton entities like the "4 main characters" can have reserved places in a shared vertex buffer rather than their separate batches.

The way I process my sprites currently are by texture: if I have a bunch of sprites using a texture, or group of similar textures for animated sprite sheets, etc, then all my sprites are listed in that sprite batch. Now, since the OpenGL specs I'm confined to at this time do not allow for the manipulation of my batches on a per object basis, I have to simulate that by copying that data into my vertices.

 

Right now, the idea is that I have a texture atlas with a bunch of images within it that my sprites can use. I link my sprite to the appropriate batch, and it usually never changes since it makes sense to stick with that batch. Now, the only way a sprite can be rendered is if it's attached to a sprite batch because it is what has access to the textures, not the sprite. I could very well have multiple batches referencing the same texture, which would simulate a quad tree as far as scene rendering goes...

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possibly 4 matrix4x4 multiplications and 4 matrix4x4 * vector3 operations. That's 48 to 64 dot products for the matrix multiplication and 12 more dot products to transform the vertices.

If your sprites don't rotate (or you classify between rotating & not rotating), you can get away with no matrix multiplication at all.
After all the transformation is just:
outPos.xy = inVertex.xy * scale.xy + position.xy;
outPos.zw = float2( -1, 1 );
That's just 1 dot product per vertex. Just make sure outPos.xy is in the [-1; 1] range.

-So, if I move the vertices out of the viewport, the GPU won't attempt to draw them? I'm still sending the data to the GPU, but if it's outside the viewport upon final transformation in the vertex shader, the pixel shader won't be processed? If I understood that correctly, then I feel better about my fill rate concerns. I'm still sending unnecessary data to the GPU, but then again 3D games are sending way more vertex data to GPU with frustum culling than you'd encounter in an entire 2D scene, generally. I would think anyway.

Yes, that's exactly what happens. Make sure all 3 vertices from the triangle lay outside the viewport. But don't make the number too big (i.e. don't place it at 8192.0 in screen coordinates; just bigger than 1.0 or less than -1.0 but not too far away; and W must not be 0)

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I like your thinking, and I do have a combiner method in my Matrix class that'll put a position and scale vector into a matrix as their elements are mutually exclusive. Rotation isn't all that common for many things, so that could be a nice workaround. The only problem is that many different types of objects 'can' rotate. What I could do is check to see if the rotation angle has changed between frames. If not, but position or scale have, then I can just use that combiner method in the class itself, possibly.

 

The code posted above does appear to be lightning fast. I'll keep that in mind for moving my triangles out of the way. When you say bigger than 1.0, is that how many pixels you suggest moving them out? My ortho matrix is based off of pixels.

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      ShaderCreationAttribs Attrs; Attrs.Desc.Name = "MyPixelShader"; Attrs.FilePath = "MyShaderFile.fx"; Attrs.SearchDirectories = "shaders;shaders\\inc;"; Attrs.EntryPoint = "MyPixelShader"; Attrs.Desc.ShaderType = SHADER_TYPE_PIXEL; Attrs.SourceLanguage = SHADER_SOURCE_LANGUAGE_HLSL; BasicShaderSourceStreamFactory BasicSSSFactory(Attrs.SearchDirectories); Attrs.pShaderSourceStreamFactory = &BasicSSSFactory; ShaderVariableDesc ShaderVars[] = {     {"g_StaticTexture", SHADER_VARIABLE_TYPE_STATIC},     {"g_MutableTexture", SHADER_VARIABLE_TYPE_MUTABLE},     {"g_DynamicTexture", SHADER_VARIABLE_TYPE_DYNAMIC} }; Attrs.Desc.VariableDesc = ShaderVars; Attrs.Desc.NumVariables = _countof(ShaderVars); Attrs.Desc.DefaultVariableType = SHADER_VARIABLE_TYPE_STATIC; StaticSamplerDesc StaticSampler; StaticSampler.Desc.MinFilter = FILTER_TYPE_LINEAR; StaticSampler.Desc.MagFilter = FILTER_TYPE_LINEAR; StaticSampler.Desc.MipFilter = FILTER_TYPE_LINEAR; StaticSampler.TextureName = "g_MutableTexture"; Attrs.Desc.NumStaticSamplers = 1; Attrs.Desc.StaticSamplers = &StaticSampler; ShaderMacroHelper Macros; Macros.AddShaderMacro("USE_SHADOWS", 1); Macros.AddShaderMacro("NUM_SHADOW_SAMPLES", 4); Macros.Finalize(); Attrs.Macros = Macros; RefCntAutoPtr<IShader> pShader; m_pDevice->CreateShader( Attrs, &pShader );
      Creating the Pipeline State Object
      After all required shaders are created, the rest of the fields of the PipelineStateDesc structure provide depth-stencil, rasterizer, and blend state descriptions, the number and format of render targets, input layout format, etc. For instance, rasterizer state can be described as follows:
      PipelineStateDesc PSODesc; RasterizerStateDesc &RasterizerDesc = PSODesc.GraphicsPipeline.RasterizerDesc; RasterizerDesc.FillMode = FILL_MODE_SOLID; RasterizerDesc.CullMode = CULL_MODE_NONE; RasterizerDesc.FrontCounterClockwise = True; RasterizerDesc.ScissorEnable = True; RasterizerDesc.AntialiasedLineEnable = False; Depth-stencil and blend states are defined in a similar fashion.
      Another important thing that pipeline state object encompasses is the input layout description that defines how inputs to the vertex shader, which is the very first shader stage, should be read from the memory. Input layout may define several vertex streams that contain values of different formats and sizes:
      // Define input layout InputLayoutDesc &Layout = PSODesc.GraphicsPipeline.InputLayout; LayoutElement TextLayoutElems[] = {     LayoutElement( 0, 0, 3, VT_FLOAT32, False ),     LayoutElement( 1, 0, 4, VT_UINT8, True ),     LayoutElement( 2, 0, 2, VT_FLOAT32, False ), }; Layout.LayoutElements = TextLayoutElems; Layout.NumElements = _countof( TextLayoutElems ); Finally, pipeline state defines primitive topology type. When all required members are initialized, a pipeline state object can be created by IRenderDevice::CreatePipelineState() method:
      // Define shader and primitive topology PSODesc.GraphicsPipeline.PrimitiveTopologyType = PRIMITIVE_TOPOLOGY_TYPE_TRIANGLE; PSODesc.GraphicsPipeline.pVS = pVertexShader; PSODesc.GraphicsPipeline.pPS = pPixelShader; PSODesc.Name = "My pipeline state"; m_pDev->CreatePipelineState(PSODesc, &m_pPSO); When PSO object is bound to the pipeline, the engine invokes all API-specific commands to set all states specified by the object. In case of Direct3D12 this maps directly to setting the D3D12 PSO object. In case of Direct3D11, this involves setting individual state objects (such as rasterizer and blend states), shaders, input layout etc. In case of OpenGL, this requires a number of fine-grain state tweaking calls. Diligent Engine keeps track of currently bound states and only calls functions to update these states that have actually changed.
      Binding Shader Resources
      Direct3D11 and OpenGL utilize fine-grain resource binding models, where an application binds individual buffers and textures to certain shader or program resource binding slots. Direct3D12 uses a very different approach, where resource descriptors are grouped into tables, and an application can bind all resources in the table at once by setting the table in the command list. Resource binding model in Diligent Engine is designed to leverage this new method. It introduces a new object called shader resource binding that encapsulates all resource bindings required for all shaders in a certain pipeline state. It also introduces the classification of shader variables based on the frequency of expected change that helps the engine group them into tables under the hood:
      Static variables (SHADER_VARIABLE_TYPE_STATIC) are variables that are expected to be set only once. They may not be changed once a resource is bound to the variable. Such variables are intended to hold global constants such as camera attributes or global light attributes constant buffers. Mutable variables (SHADER_VARIABLE_TYPE_MUTABLE) define resources that are expected to change on a per-material frequency. Examples may include diffuse textures, normal maps etc. Dynamic variables (SHADER_VARIABLE_TYPE_DYNAMIC) are expected to change frequently and randomly. Shader variable type must be specified during shader creation by populating an array of ShaderVariableDesc structures and initializing ShaderCreationAttribs::Desc::VariableDesc and ShaderCreationAttribs::Desc::NumVariables members (see example of shader creation above).
      Static variables cannot be changed once a resource is bound to the variable. They are bound directly to the shader object. For instance, a shadow map texture is not expected to change after it is created, so it can be bound directly to the shader:
      PixelShader->GetShaderVariable( "g_tex2DShadowMap" )->Set( pShadowMapSRV ); Mutable and dynamic variables are bound via a new Shader Resource Binding object (SRB) that is created by the pipeline state (IPipelineState::CreateShaderResourceBinding()):
      m_pPSO->CreateShaderResourceBinding(&m_pSRB); Note that an SRB is only compatible with the pipeline state it was created from. SRB object inherits all static bindings from shaders in the pipeline, but is not allowed to change them.
      Mutable resources can only be set once for every instance of a shader resource binding. Such resources are intended to define specific material properties. For instance, a diffuse texture for a specific material is not expected to change once the material is defined and can be set right after the SRB object has been created:
      m_pSRB->GetVariable(SHADER_TYPE_PIXEL, "tex2DDiffuse")->Set(pDiffuseTexSRV); In some cases it is necessary to bind a new resource to a variable every time a draw command is invoked. Such variables should be labeled as dynamic, which will allow setting them multiple times through the same SRB object:
      m_pSRB->GetVariable(SHADER_TYPE_VERTEX, "cbRandomAttribs")->Set(pRandomAttrsCB); Under the hood, the engine pre-allocates descriptor tables for static and mutable resources when an SRB objcet is created. Space for dynamic resources is dynamically allocated at run time. Static and mutable resources are thus more efficient and should be used whenever possible.
      As you can see, Diligent Engine does not expose low-level details of how resources are bound to shader variables. One reason for this is that these details are very different for various APIs. The other reason is that using low-level binding methods is extremely error-prone: it is very easy to forget to bind some resource, or bind incorrect resource such as bind a buffer to the variable that is in fact a texture, especially during shader development when everything changes fast. Diligent Engine instead relies on shader reflection system to automatically query the list of all shader variables. Grouping variables based on three types mentioned above allows the engine to create optimized layout and take heavy lifting of matching resources to API-specific resource location, register or descriptor in the table.
      This post gives more details about the resource binding model in Diligent Engine.
      Setting the Pipeline State and Committing Shader Resources
      Before any draw or compute command can be invoked, the pipeline state needs to be bound to the context:
      m_pContext->SetPipelineState(m_pPSO); Under the hood, the engine sets the internal PSO object in the command list or calls all the required native API functions to properly configure all pipeline stages.
      The next step is to bind all required shader resources to the GPU pipeline, which is accomplished by IDeviceContext::CommitShaderResources() method:
      m_pContext->CommitShaderResources(m_pSRB, COMMIT_SHADER_RESOURCES_FLAG_TRANSITION_RESOURCES); The method takes a pointer to the shader resource binding object and makes all resources the object holds available for the shaders. In the case of D3D12, this only requires setting appropriate descriptor tables in the command list. For older APIs, this typically requires setting all resources individually.
      Next-generation APIs require the application to track the state of every resource and explicitly inform the system about all state transitions. For instance, if a texture was used as render target before, while the next draw command is going to use it as shader resource, a transition barrier needs to be executed. Diligent Engine does the heavy lifting of state tracking.  When CommitShaderResources() method is called with COMMIT_SHADER_RESOURCES_FLAG_TRANSITION_RESOURCES flag, the engine commits and transitions resources to correct states at the same time. Note that transitioning resources does introduce some overhead. The engine tracks state of every resource and it will not issue the barrier if the state is already correct. But checking resource state is an overhead that can sometimes be avoided. The engine provides IDeviceContext::TransitionShaderResources() method that only transitions resources:
      m_pContext->TransitionShaderResources(m_pPSO, m_pSRB); In some scenarios it is more efficient to transition resources once and then only commit them.
      Invoking Draw Command
      The final step is to set states that are not part of the PSO, such as render targets, vertex and index buffers. Diligent Engine uses Direct3D11-syle API that is translated to other native API calls under the hood:
      ITextureView *pRTVs[] = {m_pRTV}; m_pContext->SetRenderTargets(_countof( pRTVs ), pRTVs, m_pDSV); // Clear render target and depth buffer const float zero[4] = {0, 0, 0, 0}; m_pContext->ClearRenderTarget(nullptr, zero); m_pContext->ClearDepthStencil(nullptr, CLEAR_DEPTH_FLAG, 1.f); // Set vertex and index buffers IBuffer *buffer[] = {m_pVertexBuffer}; Uint32 offsets[] = {0}; Uint32 strides[] = {sizeof(MyVertex)}; m_pContext->SetVertexBuffers(0, 1, buffer, strides, offsets, SET_VERTEX_BUFFERS_FLAG_RESET); m_pContext->SetIndexBuffer(m_pIndexBuffer, 0); Different native APIs use various set of function to execute draw commands depending on command details (if the command is indexed, instanced or both, what offsets in the source buffers are used etc.). For instance, there are 5 draw commands in Direct3D11 and more than 9 commands in OpenGL with something like glDrawElementsInstancedBaseVertexBaseInstance not uncommon. Diligent Engine hides all details with single IDeviceContext::Draw() method that takes takes DrawAttribs structure as an argument. The structure members define all attributes required to perform the command (primitive topology, number of vertices or indices, if draw call is indexed or not, if draw call is instanced or not, if draw call is indirect or not, etc.). For example:
      DrawAttribs attrs; attrs.IsIndexed = true; attrs.IndexType = VT_UINT16; attrs.NumIndices = 36; attrs.Topology = PRIMITIVE_TOPOLOGY_TRIANGLE_LIST; pContext->Draw(attrs); For compute commands, there is IDeviceContext::DispatchCompute() method that takes DispatchComputeAttribs structure that defines compute grid dimension.
      Source Code
      Full engine source code is available on GitHub and is free to use. The repository contains tutorials, sample applications, asteroids performance benchmark and an example Unity project that uses Diligent Engine in native plugin.
      Atmospheric scattering sample demonstrates how Diligent Engine can be used to implement various rendering tasks: loading textures from files, using complex shaders, rendering to multiple render targets, using compute shaders and unordered access views, etc.

      Asteroids performance benchmark is based on this demo developed by Intel. It renders 50,000 unique textured asteroids and allows comparing performance of Direct3D11 and Direct3D12 implementations. Every asteroid is a combination of one of 1000 unique meshes and one of 10 unique textures.

      Finally, there is an example project that shows how Diligent Engine can be integrated with Unity.

      Future Work
      The engine is under active development. It currently supports Windows desktop, Universal Windows, Linux, Android, MacOS, and iOS platforms. Direct3D11, Direct3D12, OpenGL/GLES backends are now feature complete. Vulkan backend is coming next, and Metal backend is in the plan.
    • By LifeArtist
      Good Evening,
      I want to make a 2D game which involves displaying some debug information. Especially for collision, enemy sights and so on ...
      First of I was thinking about all those shapes which I need will need for debugging purposes: circles, rectangles, lines, polygons.
      I am really stucked right now because of the fundamental question:
      Where do I store my vertices positions for each line (object)? Currently I am not using a model matrix because I am using orthographic projection and set the final position within the VBO. That means that if I add a new line I would have to expand the "points" array and re-upload (recall glBufferData) it every time. The other method would be to use a model matrix and a fixed vbo for a line but it would be also messy to exactly create a line from (0,0) to (100,20) calculating the rotation and scale to make it fit.
      If I proceed with option 1 "updating the array each frame" I was thinking of having 4 draw calls every frame for the lines vao, polygons vao and so on. 
      In addition to that I am planning to use some sort of ECS based architecture. So the other question would be:
      Should I treat those debug objects as entities/components?
      For me it would make sense to treat them as entities but that's creates a new issue with the previous array approach because it would have for example a transform and render component. A special render component for debug objects (no texture etc) ... For me the transform component is also just a matrix but how would I then define a line?
      Treating them as components would'nt be a good idea in my eyes because then I would always need an entity. Well entity is just an id !? So maybe its a component?
      Regards,
      LifeArtist
    • By QQemka
      Hello. I am coding a small thingy in my spare time. All i want to achieve is to load a heightmap (as the lowest possible walking terrain), some static meshes (elements of the environment) and a dynamic character (meaning i can move, collide with heightmap/static meshes and hold a varying item in a hand ). Got a bunch of questions, or rather problems i can't find solution to myself. Nearly all are deal with graphics/gpu, not the coding part. My c++ is on high enough level.
      Let's go:
      Heightmap - i obviously want it to be textured, size is hardcoded to 256x256 squares. I can't have one huge texture stretched over entire terrain cause every pixel would be enormous. Thats why i decided to use 2 specified textures. First will be a tileset consisting of 16 square tiles (u v range from 0 to 0.25 for first tile and so on) and second a 256x256 buffer with 0-15 value representing index of the tile from tileset for every heigtmap square. Problem is, how do i blend the edges nicely and make some computationally cheap changes so its not obvious there are only 16 tiles? Is it possible to generate such terrain with some existing program?
      Collisions - i want to use bounding sphere and aabb. But should i store them for a model or entity instance? Meaning i have 20 same trees spawned using the same tree model, but every entity got its own transformation (position, scale etc). Storing collision component per instance grats faster access + is precalculated and transformed (takes additional memory, but who cares?), so i stick with this, right? What should i do if object is dynamically rotated? The aabb is no longer aligned and calculating per vertex min/max everytime object rotates/scales is pretty expensive, right?
      Drawing aabb - problem similar to above (storing aabb data per instance or model). This time in my opinion per model is enough since every instance also does not have own vertex buffer but uses the shared one (so 20 trees share reference to one tree model). So rendering aabb is about taking the model's aabb, transforming with instance matrix and voila. What about aabb vertex buffer (this is more of a cosmetic question, just curious, bumped onto it in time of writing this). Is it better to make it as 8 points and index buffer (12 lines), or only 2 vertices with min/max x/y/z and having the shaders dynamically generate 6 other vertices and draw the box? Or maybe there should be just ONE 1x1x1 cube box template moved/scaled per entity?
      What if one model got a diffuse texture and a normal map, and other has only diffuse? Should i pass some bool flag to shader with that info, or just assume that my game supports only diffuse maps without fancy stuff?
      There were several more but i forgot/solved them at time of writing
      Thanks in advance
    • By RenanRR
      Hi All,
      I'm reading the tutorials from learnOpengl site (nice site) and I'm having a question on the camera (https://learnopengl.com/Getting-started/Camera).
      I always saw the camera being manipulated with the lookat, but in tutorial I saw the camera being changed through the MVP arrays, which do not seem to be camera, but rather the scene that changes:
      Vertex Shader:
      #version 330 core layout (location = 0) in vec3 aPos; layout (location = 1) in vec2 aTexCoord; out vec2 TexCoord; uniform mat4 model; uniform mat4 view; uniform mat4 projection; void main() { gl_Position = projection * view * model * vec4(aPos, 1.0f); TexCoord = vec2(aTexCoord.x, aTexCoord.y); } then, the matrix manipulated:
      ..... glm::mat4 projection = glm::perspective(glm::radians(fov), (float)SCR_WIDTH / (float)SCR_HEIGHT, 0.1f, 100.0f); ourShader.setMat4("projection", projection); .... glm::mat4 view = glm::lookAt(cameraPos, cameraPos + cameraFront, cameraUp); ourShader.setMat4("view", view); .... model = glm::rotate(model, glm::radians(angle), glm::vec3(1.0f, 0.3f, 0.5f)); ourShader.setMat4("model", model);  
      So, some doubts:
      - Why use it like that?
      - Is it okay to manipulate the camera that way?
      -in this way, are not the vertex's positions that changes instead of the camera?
      - I need to pass MVP to all shaders of object in my scenes ?
       
      What it seems, is that the camera stands still and the scenery that changes...
      it's right?
       
       
      Thank you
       
    • By dpadam450
      Sampling a floating point texture where the alpha channel holds 4-bytes of packed data into the float. I don't know how to cast the raw memory to treat it as an integer so I can perform bit-shifting operations.

      int rgbValue = int(textureSample.w);//4 bytes of data packed as color
      // algorithm might not be correct and endianness might need switching.
      vec3 extractedData = vec3(  rgbValue & 0xFF000000,  (rgbValue << 8) & 0xFF000000, (rgbValue << 16) & 0xFF000000);
      extractedData /= 255.0f;
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