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OpenGL OpenGL for high school

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At the high school where we work, I have been approached about offering a class in Computer Graphics for the students. Initially, I felt this topic would be too advanced, but my students are pretty smart. I think I'll be cutting out a lot of the theory and mathematics involved and focus more on OpenGL programming. Each student that takes this will need to have completed (with an 85% or better) our Introduction to Computer Science class, which is the equivalent of a Programming I and II university classes. I don't believe OpenGL will be much trouble for them. Right now, we use Microsoft's Visual C++ 2005 Express as our IDE and compiler. Naturally, we use C++ and will do so in the Graphics class. Any suggestions or ideas on this class? Anything from projects, structure, general implementation is welcome. I had a thought of using Nehe's tutorials from nehe.gamedev.net, but it's been said that that may be too advanced initally. Text wise, I'm planning on using the red book, but I welcome any further suggestions.

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I think the redbook should be used like a text book and you should adapt the NeHe tutorials into lesson plans... I am at high school age and learnt opengl from NeHe's tutorials.

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I don't think you should use NeHe's actual code as basis, although the progression of the tutorials is probably acceptable for a lesson plan.

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Guest Anonymous Poster
Quote:
Original post by taesen00
I think I'll be cutting out a lot of the theory and mathematics involved and focus more on OpenGL programming.



I really think that a good understanding of the Theory (and math, but theory moreso) is important for effective use of OpenGL.
Far too often beginners get into trouble when the know how to copy and paste opengl api calls from tutorials, but really have no idea what's going on behind the scenes. ("why won't my rotations work in the right order?",etc)

If I remember correctly, late HS is about when students start learning about matrices and linear algebra; both of which tie directly into the math and theory behind opengl. It's a perfect opportunity to illustrate to them the practical usage of the stuff from math class...

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I would start off by showing advanced concepts. Describing arictecture first, going through open sourced engines(Quake 1). I would skip some of theory, but still apply basic concepts. Example rendering triangles, creating a cube, etc. Then I would jump from there to loading BSP trees. For a high school class, I don't think its important to manually draw worlds, or shapes in general.

One thing thats important is to see the relationship between Level editors and a opengl renderer. Stick with simple lighting such as pre-generated lightmaps, and bring UP OpenGL shaders, say what there used for, and make students learn that on there own if they wish. Offer it like extra credit. Students should know how lists work, and same with extensions.

Once your past the basics, you should know introduce a pre-done framework that does logging, file handling, etc, sense that stuff is not exactlly what that class is all about.

Translating worlds is important, for camera movements. It seems like this would be a AP level class, so I don't think its unreasonable for students to adding a gaming layer on there own to pass commands to a rendering class.

Thats just some ideas, I would require the students to demonstrate they know C++ kind of fluentlly and know OOP. They should know strong concepts of pointers as well, and how memory is used.

If its a year class I would keep more of theory, but if its a semester class, your going to need to drop alot of the nit picky stuff. it is very important to know what is going on behind the scenes, but it should be more of a college class that fills in those gaps, while you just go over some of those gaps if that makes sense.

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Guest Anonymous Poster
Quote:
Original post by eviltwigflipper
I would start off by showing advanced concepts. Describing arictecture first, going through open sourced engines(Quake 1). I would skip some of theory, but still apply basic concepts. Example rendering triangles, creating a cube, etc. Then I would jump from there to loading BSP trees. For a high school class, I don't think its important to manually draw worlds, or shapes in general.

One thing thats important is to see the relationship between Level editors and a opengl renderer. Stick with simple lighting such as pre-generated lightmaps, and bring UP OpenGL shaders, say what there used for, and make students learn that on there own if they wish. Offer it like extra credit. Students should know how lists work, and same with extensions.

Once your past the basics, you should know introduce a pre-done framework that does logging, file handling, etc, sense that stuff is not exactlly what that class is all about.

Translating worlds is important, for camera movements. It seems like this would be a AP level class, so I don't think its unreasonable for students to adding a gaming layer on there own to pass commands to a rendering class.

Thats just some ideas, I would require the students to demonstrate they know C++ kind of fluentlly and know OOP. They should know strong concepts of pointers as well, and how memory is used.

If its a year class I would keep more of theory, but if its a semester class, your going to need to drop alot of the nit picky stuff. it is very important to know what is going on behind the scenes, but it should be more of a college class that fills in those gaps, while you just go over some of those gaps if that makes sense.



Yeah... if you want to teach them to be a bunch of Modders
I suggest a more 'academic' approach. There is more to OpenGL than first person shooters. Why not delve into the field of Scientific Visualization?

a simple first lesson might be:
given this Real topographic elevation data, let's create a 3d model of this section of land; and color code it based on elevation.
Now lets color it based on the slope of the land. Combine that data to decide what locations the following type of tree can grow, now render the trees(simple billboards).
Doesn't that sound much more educational than "lets learn how to load a quake map"?

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Guest Anonymous Poster
...
and as a Special Surprise, at the end once the 'serious' landscape task is finished, introduce them to moving the camera via mouselook, add simple collision detection, and let them 'walk' across it - the beggingings of a simple first person shooter.

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Start showing them some features that will motivate them to use OpenGL (no in depth explanation, just showing what is possible).

Then start with the basics: setting up an application, render a triangle, render some more complex object, moving objects around (simple matrix ops) etc.
It doesn't make sense to jump right into advanced concepts like level loading or BSP-Trees if they won't even have an idea of what they mean and what is behind them.

Your students should be familiar with matrix and vector math to some degree but you could show them how to do transformations and why the order of transformation is important (like scaling x rotation x translation).

Then if they got the basics start a course project by developing some simple engine (for whatever purpose you want). Have the students discuss features and possible implementations. Teach them application architecture and have them make a decision on which architecture to use.

Overall, you should always try not to have too long boring periods in which only theory or basic coding (code that doesn't have any conceivable use for the students) prevails. Try to keep them motivated by having them experience their own little successes until they master the basics. Then they should be able to start the engine project.

At the end of the class you finally could propose writing some term papers on advanced concepts like BSP-Trees, SceneGraphs etc. and have the students implement them into their engine. Up to then they should have the knowledge they need to dig further into 3D design.

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if u do go with nehe
make sure u go with the glut version + not the win32 version

download both versions to see why

certainly better than what i got at school http://en.wikipedia.org/wiki/Logo_programming_language

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Wow, you guys offer OpenGL as a class? I wish my HS offered it, all we have is Programming I which is way to easy for me :(.

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Quote:
Original post by Anonymous Poster
Yeah... if you want to teach them to be a bunch of Modders
I suggest a more 'academic' approach. There is more to OpenGL than first person shooters. Why not delve into the field of Scientific Visualization?


Four words: Scientific Visuzation is boring. You need to make it interesting, and give them a broad range of game programming, they can get more specilized training when they take a college course. We need more computer science majors, if you burden your students with a bunch of theory there not going to be as interested.

OpenGL commands if your not doing stuff thats high-tech is pretty straight foward. The design and arctecture aspect should be what you focus is on.

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Let me clear up when I say I plan on taking out a lot of theory and math.

By that, I mean for beginners, they wouldn't need to know something like Bresenham's Line-Drawing Algorithm, or integrals (since some of them may not have yet taken Calculus). However, of course I'm going to keep a lot of Linear Algebra in there. Matrix multiplication order is important.

Now, I do have this to my advantange: I have taught most of them in Honors Geometry as freshmen. When I was asked to teach Computer Science as well, I started gearing my classes towards programming concepts. Hence, indepth lessons on Boolean logic and transformations. So I know the majority of them have already had some experience with matrix algebra and its applications to Computer Graphics. We did some programs in Maple to see how their transformation matrices affected their shapes.

For those curious, here's a tenative course listing for the Computer Science curriculum at our high school:

Intro to Computer Science: basically university Programming I and II in C++.

AP Computer Science: Standard AP CS class in Java. Will move a little faster because the students will already be familiar with a great deal of the concepts from the Intro class.

Advanced Topics in CS: This class will be stuff that I want to teach. Students can repeat this course for credit as the topics will change from year to year. Next year, I plan on OpenGL. The year after, I think I will teach AI.

Naturally, we have stuff like Web Design, Digital Media, and the classic "How to Use Microsoft Office" class.

Once students complete the Intro class (with and 85% or better), they will be eligible to take the Advanced Topics class.

So far, everyone has had some great ideas for the OpenGL class, and I look forward to implementing a number of them. If you have any more thoughts or suggestions, keep them coming.

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This is our first year to implement this CS program, so the only really set plans are for the Intro to CS class. I have an idea for the OpenGL version of the Advanced Topics class. I'll be happy to share those with you, and welcome any feedback. For an AP CS outline, it's available at apcentral.collegeboard.com.
Here we go:

Introduction to Computer Science (C++)
**************************************************************
These topics are listed in the order I intend to cover them
***************************************************************
Basic Terms
Introduction to Algorithms
Functions of a Computer
Variables
Basic I/O
Integer Arithmetic
Conditional Statements
Boolean Logic
While Loops
Floating Point Arithmetic
I/O Manipulation
For and Do-While loops
Understanding the Input Buffer
Switch Statements
Functions
Arrays
Constants and Macros
Text File I/O
Sorting
Strings
Command Line Arguments
Structs
2D Arrays
Pointers
Linked Lists
Binary Files
Recusion
Algorithm Analysis
Binary Search
Stacks
Queues
Beginning OOP

AP CS
********************************************
As you can see above, they will have a good bit of experience with most concepts by the time they finish Intro, and even a little bit of dabbling into OOP. So for this class, in addition to the basic AP stuff, I'm gonna go more indepth with topics like sorting algorithms and algorithm analysis, to name a few.
********************************************

Advanced Topics in CS
*******************************************
This class will change from year to year. Next year, I'm going to cover OpenGL because some of the students are juniors this year, and that's what they want to study. This class is still very much in development, and I have yet to incorporate ideas mentioned in earlier posts by others, but this is a tentative list of topics. I think this would cover a semester or a little more, but once they learn these basics, I want to get into some really cool stuff.
********************************************
Basic terms
GLUT callback functions
Basic set up of an OpenGL program
Installing and compiling OpenGL at home
The World and World Window
Single and Double buffering
Line Clipping and Algoritms
GLUI
Vectors and Dot products
Linear Interpolation
Tweening and Quadratic tweening
Parametric forms of lines
Intersection of Line Segments
Line Clipping Against a Convex Polygon Algorithms (probably Cyrus-Beck)
Homogeneous Coordinates
Cross products
Matrix Transformations
OpenGL pipeline (simplified)
Viewport transformations
Perspective Division
glMatrixMode();
Matrix stacks
Z-buffer
Light in OpenGL
Material Properties

And there you have it.


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Towards the end I would show how to load up a world(like Quake 3), and just draw the geoemtry(ignore pvs, collision, etc). And show how texture blending works(probley a good idea to have a day lesson on how this works including the stuff behind the scenes). Then also show how to blend lightmaps on top of the diffuse texture. When they leave the class besides all the stuff you said above, they should see the relationship between a world editor and rendering engine.

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I would go one step further for another advanced rendering class after your first one that teaches them the basics of OpenGL. Make an entire semester based on creating a software renderer based on the OpenGL API. This will give your students the best understanding of what goes on under the hood of a graphics card. This approach might be dated, but I enjoyed every minute of it when I took this type of class in college.

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So did I, and I still regularly work on software renderers.

However, don't think it's really appropriate for a high-school level course. High school students are more likely to want to see interesting results to keep themselves interested, and many of them suffer the "prima donna" syndrome that they'll be carrying into their first few years of college where they refuse to see how an understanding of the "under the hood" mechanics will help them.

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Quote:
Original post by Anonymous Poster
Quote:
Original post by taesen00
I think I'll be cutting out a lot of the theory and mathematics involved and focus more on OpenGL programming.



I really think that a good understanding of the Theory (and math, but theory moreso) is important for effective use of OpenGL.
Far too often beginners get into trouble when the know how to copy and paste opengl api calls from tutorials, but really have no idea what's going on behind the scenes. ("why won't my rotations work in the right order?",etc)

If I remember correctly, late HS is about when students start learning about matrices and linear algebra; both of which tie directly into the math and theory behind opengl. It's a perfect opportunity to illustrate to them the practical usage of the stuff from math class...


I really second that. I've been programming OpenGL since I was fourteen. Now I'm 20 and studying, and the math that is being thought (linear algebra, matrices, vectors, bezier patches, etc. etc.) is really improving my OpenGL. I thought I knew OpenGL before I went to the university, but I'm now a much better 3D programmer than I was before, even though I didn't learn a single OpenGL API call in school. OpenGL is really a great way to put math into practise, and it helped me a lot with understanding the abstract things behind it. The basics of OpenGL aren't that hard, especially not once you have *finally* set up a window for the first time. I think I would be a good thing to really balance the math with the OpenGL (in this case, more math, less/same opengl)

I hope this helps you a bit :)

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Personally, I think if you're going to teach them about 3D graphics without even talking about texture mapping, you're making a big mistake. ;) It's not that complex, but it adds a world of complexity to any 3D game. If you're going to use the Red Book, I'd go through Chapter 1, 2 (skipping arrays), 3, 4 (including alpha), 5, 6, 9, and 10 (skipping accumulation buffer talk). That's pretty good coverage with some advanced topics thrown in while keeping it simple enough (I think) for any high school student. Because those were the chapters I understood in HS. Here's how I would structure the class:

Basic terms
GLUT callback functions
Basic set up of an OpenGL program
Installing and compiling OpenGL at home
The World and World Window
Single and Double buffering
Line Clipping and Algoritms (I would only discuss polygonal culling and only after cross/dot products)
GLUI
Vectors and Dot products (and Cross Products)
Linear Interpolation
Parametric forms of lines
Intersection of Line Segments
Homogeneous Coordinates (do it if you have time left over)
Matrix Transformations
OpenGL pipeline (simplified)
Z-Buffering
Polygonal culling, depth testing, etc
Viewport transformations
Perspective Division
glMatrixMode();
Matrix stacks
Light in OpenGL
Material Properties
Texture Mapping

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If I were teaching the class, I would create 7 or 8 sections.

The important thing at this level is to give the students working code so that you can focus on important concepts.

Start with a framework that
* renders the unit cube.
* already has an infinite light source
* has some basic user feedback controls built in to move the camera
* has any file loading routines such as loading of a bitmap or a 3d model already written and included.

Just code this up yourself, or get it out of one of those beginning game programming books, clean it up a bit and give it to the students.

For each lesson plan describe a graphics feature such as vertex coordinates.
Give the homework task of implementing something with that feature.

For each lesson build on the previous lesson code.

I would do lessons in something like this order

Vertex coordinates and 3d space
Camera Introduction
Colors and Materials
Textures
Lighting
User Feedback
Performance considerations
Advanced Topics

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I never liked the red book. I used Beginning OpenGL Game Programming by Dave Astle and Kevin Kawkins (i believe they run gamedev.net). In my opinion, this book is the best book to learn openGL. I suggest you teach your class out of this book.

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      Device resources are created by the render device. The two main resource types are buffers, which represent linear memory, and textures, which use memory layouts optimized for fast filtering. Graphics APIs usually have a native object that represents linear buffer. Diligent Engine uses IBuffer interface as an abstraction for a native buffer. To create a buffer, one needs to populate BufferDesc structure and call IRenderDevice::CreateBuffer() method as in the following example:
      BufferDesc BuffDesc; BufferDesc.Name = "Uniform buffer"; BuffDesc.BindFlags = BIND_UNIFORM_BUFFER; BuffDesc.Usage = USAGE_DYNAMIC; BuffDesc.uiSizeInBytes = sizeof(ShaderConstants); BuffDesc.CPUAccessFlags = CPU_ACCESS_WRITE; m_pDevice->CreateBuffer( BuffDesc, BufferData(), &m_pConstantBuffer ); While there is usually just one buffer object, different APIs use very different approaches to represent textures. For instance, in Direct3D11, there are ID3D11Texture1D, ID3D11Texture2D, and ID3D11Texture3D objects. In OpenGL, there is individual object for every texture dimension (1D, 2D, 3D, Cube), which may be a texture array, which may also be multisampled (i.e. GL_TEXTURE_2D_MULTISAMPLE_ARRAY). As a result there are nine different GL texture types that Diligent Engine may create under the hood. In Direct3D12, there is only one resource interface. Diligent Engine hides all these details in ITexture interface. There is only one  IRenderDevice::CreateTexture() method that is capable of creating all texture types. Dimension, format, array size and all other parameters are specified by the members of the TextureDesc structure:
      TextureDesc TexDesc; TexDesc.Name = "My texture 2D"; TexDesc.Type = TEXTURE_TYPE_2D; TexDesc.Width = 1024; TexDesc.Height = 1024; TexDesc.Format = TEX_FORMAT_RGBA8_UNORM; TexDesc.Usage = USAGE_DEFAULT; TexDesc.BindFlags = BIND_SHADER_RESOURCE | BIND_RENDER_TARGET | BIND_UNORDERED_ACCESS; TexDesc.Name = "Sample 2D Texture"; m_pRenderDevice->CreateTexture( TexDesc, TextureData(), &m_pTestTex ); If native API supports multithreaded resource creation, textures and buffers can be created by multiple threads simultaneously.
      Interoperability with native API provides access to the native buffer/texture objects and also allows creating Diligent Engine objects from native handles. It allows applications seamlessly integrate native API-specific code with Diligent Engine.
      Next-generation APIs allow fine level-control over how resources are allocated. Diligent Engine does not currently expose this functionality, but it can be added by implementing IResourceAllocator interface that encapsulates specifics of resource allocation and providing this interface to CreateBuffer() or CreateTexture() methods. If null is provided, default allocator should be used.
      Initializing the Pipeline State
      As it was mentioned earlier, Diligent Engine follows next-gen APIs to configure the graphics/compute pipeline. One big Pipelines State Object (PSO) encompasses all required states (all shader stages, input layout description, depth stencil, rasterizer and blend state descriptions etc.). This approach maps directly to Direct3D12/Vulkan, but is also beneficial for older APIs as it eliminates pipeline misconfiguration errors. With many individual calls tweaking various GPU pipeline settings it is very easy to forget to set one of the states or assume the stage is already properly configured when in fact it is not. Using pipeline state object helps avoid these problems as all stages are configured at once.
      Creating Shaders
      While in earlier APIs shaders were bound separately, in the next-generation APIs as well as in Diligent Engine shaders are part of the pipeline state object. The biggest challenge when authoring shaders is that Direct3D and OpenGL/Vulkan use different shader languages (while Apple uses yet another language in their Metal API). Maintaining two versions of every shader is not an option for real applications and Diligent Engine implements shader source code converter that allows shaders authored in HLSL to be translated to GLSL. To create a shader, one needs to populate ShaderCreationAttribs structure. SourceLanguage member of this structure tells the system which language the shader is authored in:
      SHADER_SOURCE_LANGUAGE_DEFAULT - The shader source language matches the underlying graphics API: HLSL for Direct3D11/Direct3D12 mode, and GLSL for OpenGL and OpenGLES modes. SHADER_SOURCE_LANGUAGE_HLSL - The shader source is in HLSL. For OpenGL and OpenGLES modes, the source code will be converted to GLSL. SHADER_SOURCE_LANGUAGE_GLSL - The shader source is in GLSL. There is currently no GLSL to HLSL converter, so this value should only be used for OpenGL and OpenGLES modes. There are two ways to provide the shader source code. The first way is to use Source member. The second way is to provide a file path in FilePath member. Since the engine is entirely decoupled from the platform and the host file system is platform-dependent, the structure exposes pShaderSourceStreamFactory member that is intended to provide the engine access to the file system. If FilePath is provided, shader source factory must also be provided. If the shader source contains any #include directives, the source stream factory will also be used to load these files. The engine provides default implementation for every supported platform that should be sufficient in most cases. Custom implementation can be provided when needed.
      When sampling a texture in a shader, the texture sampler was traditionally specified as separate object that was bound to the pipeline at run time or set as part of the texture object itself. However, in most cases it is known beforehand what kind of sampler will be used in the shader. Next-generation APIs expose new type of sampler called static sampler that can be initialized directly in the pipeline state. Diligent Engine exposes this functionality: when creating a shader, textures can be assigned static samplers. If static sampler is assigned, it will always be used instead of the one initialized in the texture shader resource view. To initialize static samplers, prepare an array of StaticSamplerDesc structures and initialize StaticSamplers and NumStaticSamplers members. Static samplers are more efficient and it is highly recommended to use them whenever possible. On older APIs, static samplers are emulated via generic sampler objects.
      The following is an example of shader initialization:
      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.
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