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OpenGL Lighting sparse meshes

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You should investigate per-pixel lighting. Instead of doing your lighting calculations in the vertex shader you do them in the pixel shader. You'll need to make a few extra tweaks, like interpolating the normal across the triangle so you have a per-pixel normal available.

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Is this a good tutorial on the subject? http://www.lighthouse3d.com/opengl/glsl/

It sounds like I have to somehow make my own vertex and fragment shader? It also sounds like it depends on what version of OpenGL I have.

gluGetString(GL_VERSION) tells me I am running 1.2.2.0 Microsoft Corporation

I would assume my machine/OS is a higher version, and this 1.2.2.0 version is the one I'm working with in my program?

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Right now I draw with these calls:
void DrawVbo()const{
glBindBufferARB(GL_ARRAY_BUFFER_ARB, Vbo_Vert_Id);
glVertexPointer(3, GL_FLOAT, 32, 0);
glNormalPointer (GL_FLOAT, 32, (GLvoid*) (NULL + sizeof (float) * 3));
glTexCoordPointer (2, GL_FLOAT, 32, (GLvoid*) (NULL + sizeof (float) * 6));
glDrawElements(GL_TRIANGLES, NumIndices(Portal_Walls.size()), GL_UNSIGNED_BYTE, 0);
}

Is this usage compatible with using fragment shader?

Do I need to use a vertex shader if I am using a fragment shader? The vertexes are fine, I just want the fragment shader.

Do I need to change to glVertexAttribPointerARB() instead?

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Quote:
Original post by PrestoChung
Is this usage compatible with using fragment shader?

of course.
however you should change gl*Pointer to glVertexAttribPointer (i think its not necessary tho)

actually i dont know wether you need a vertex shader, as i have never encountered a situation where i only needed a fragment shader.

LightHouse3D GLSL tutorial is quite good btw ;)
EDIT:
Quote:
IF you have a pair vertex/fragment of shaders you'll need to attach both to the program.

from lighthouse3d tut... looks like you dont need both. just try it.
but youll need a vertex shader anyway for interpolating the normal :PP

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Quote:
Original post by blubberbert
of course.
however you should change gl*Pointer to glVertexAttribPointer (i think its not necessary tho)


Nope, it is not necessary, but it is a good idea, since generic vertex attributes are modern.

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Thanks.

Any clue as to why glShaderSourceARB is crashing here? I adapted the file loading from this tutorial I had to change some things. Here's my adapted code:


inline Uint32 GetFileLength(std::ifstream& file_){
if(!file_.good()){
return 0;
}

file_.seekg(0, std::ios::end);
Uint32 len = file_.tellg();
file_.seekg(std::ios::beg);

return len;
}

Sint32 LoadShader(char* filename_, GLchar* source_){
std::ifstream file;
GLint len;

file.open(filename_, std::ios::in); //open ASCII
if(!file){
return -1;
}

len = GetFileLength(file);

if( len==0 ){
return -2; //Is empty
}

source_ = new GLchar[len+1];

if ( *source_==0 ){
return -3; //Memory not reserved
}

source_[len] = '\0';

Uint32 i = 0;

while( file.good() ){
source_[i] = (GLchar)file.get(); //Get character from file
if( !file.eof() ){
++i;
}
}

source_[i] = '\0'; //0-terminate at correct position

file.close();

return 0; //No errors
}

CompileShaders(){
GLhandleARB vshadehandle;
GLhandleARB fshadehandle;
GLcharARB* vshadesource=0;
GLcharARB* fshadesource=0;
vshadehandle = glCreateShaderObjectARB(GL_VERTEX_SHADER_ARB );
fshadehandle = glCreateShaderObjectARB(GL_FRAGMENT_SHADER_ARB );
LoadShader("vertshader.vert", vshadesource );
LoadShader("fragshader.frag", fshadesource );
glShaderSourceARB(vshadehandle, 1, (const GLcharARB**)&vshadesource, NULL); //<-----CRASH
glShaderSourceARB(fshadehandle, 1, (const GLcharARB**)&fshadesource, NULL);
glCompileShaderARB(vshadehandle);
glCompileShaderARB(fshadehandle);
}



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check wether the extension is supported on your graphics card(it should be o.0)

anyway check your file loading code... it looks strange to me
Quote:
Original post by PrestoChung
if ( *source_==0 ){
return -3; //Memory not reserved
}

are you sure you want the content of source?? because after a new[] you dont know whats in there so why check it for 0?


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Ah, yes thanks for catching that. The function in the tutorial had source as a GLchar**, I have changed it to GLchar* and missed to change that part.

Doesn't seem to be related to my crash error though.

How do I check that my video card supports it? I have a newer card Geforce GTS250 i think it is.

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O, yea I have looked at that and GLEW has pulled in the proper extensions as far as I can see. I think it would tell me that the function is undefined if that was the problem.

Edit:
I just noticed in the debugger that the vshadesource and fshadesource pointers are still at 0 when I get to glShaderSourceARB so it must be a failure of of the loading function. I'll step through it and see what I can find out.

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Fixed by passing the source pointer by reference. It looks funny though
Sint32 LoadShader(char* filename_, GLchar*& source_)


Compiled successfully. Now I just need to get glDrawElements to work without crashing.

Edit: Ack! forgot to create the shader program :)

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It's working now but I'm a little confused because:

Even if my vert shader or frag shader does not compile, or contains and empty main function that does nothing, I still get some drawing.

I set 3 attrib pointers (interleaved), but nowhere do I specify that the first one is the position.

Does OpenGL automatically use the first attribute as a position vertex?

Otherwise I'm a little confused as to how it could know how to render my VBO data.

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Might this have something to do with it? Quote from http://www.opengl.org/sdk/docs/tutorials/ClockworkCoders/attributes.php

Quote:
In other words, NVidia hardware indices are reserved for built-in attributes:
gl_Vertex 0
gl_Normal 2
gl_Color 3
gl_SecondaryColor 4
gl_FogCoord 5
gl_MultiTexCoord0 8
gl_MultiTexCoord1 9
gl_MultiTexCoord2 10
gl_MultiTexCoord3 11
gl_MultiTexCoord4 12
gl_MultiTexCoord5 13
gl_MultiTexCoord6 14
gl_MultiTexCoord7 15


When enable or set an attribute pointer
glEnableVertexAttribArray(0);
glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, sizeof(TexNormVert), 0);

in this case attribute "0", whenever I use gl_Vertex in my shader source, it is looking at this attribute?

It seems to be so. When I use attribute 8 for the texture coordinate part of my Vertex
glEnableVertexAttribArray(8);
glVertexAttribPointer(8, 2, GL_FLOAT, GL_FALSE, sizeof(TexNormVert), (GLvoid*) (NULL + sizeof (GL_FLOAT) * 6) );

I suddenly get texture to display properly!

This shader code is generating an error C5052: gl_MultiTexCoord0 is not accessible in this profile

But at the same time the texture is rendering! I'm really mystified as to how this is possible.

vertshader.vert
void main()
{
gl_Position = ftransform();
}
fragshader.frag
uniform sampler2D tex;

void main()
{
gl_FragColor = texture2D(tex, gl_MultiTexCoord0);
}

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Edit: updated a bit. Still no drawing visible:

Here is setup after shaders are compiled:
Shader_Program = glCreateProgramObjectARB();
glAttachObjectARB(Shader_Program, vshadehandle);
glAttachObjectARB(Shader_Program, fshadehandle);

glBindAttribLocationARB( Shader_Program, 0, "inVertex" );
glBindAttribLocationARB( Shader_Program, 1, "inNormal" );
glBindAttribLocationARB( Shader_Program, 2, "inTexCoord0" );
glBindFragDataLocation( Shader_Program, 0, "outFragColor" );

glLinkProgramARB( Shader_Program );
glUseProgramObjectARB( Shader_Program );



Here is building VAO and VBO for each object:
glGenVertexArrays(1, &Vao_Handle);
glBindVertexArray(Vao_Handle);

glGenBuffersARB(1, &Vbo_Handle);
glBindBufferARB(GL_ARRAY_BUFFER_ARB, Vbo_Handle);
glBufferDataARB(GL_ARRAY_BUFFER_ARB, sizeof(vertices[0])*vertices.size(), &vertices[0], GL_STATIC_DRAW_ARB);

glEnableVertexAttribArray(0);
glEnableVertexAttribArray(1);
glEnableVertexAttribArray(2);
glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, sizeof(TexNormVert), 0);
glVertexAttribPointer(1, 3, GL_FLOAT, GL_TRUE, sizeof(TexNormVert), (GLvoid*) (NULL + sizeof (GL_FLOAT) * 3) );
glVertexAttribPointer(2, 2, GL_FLOAT, GL_FALSE, sizeof(TexNormVert), (GLvoid*) (NULL + sizeof (GL_FLOAT) * 6) );

glBindBufferARB(GL_ELEMENT_ARRAY_BUFFER_ARB, Vbo_Element_Index);

glBindVertexArray(0);

Then the drawing step:
glBindVertexArray(Vao_Handle);
glDrawElements(GL_TRIANGLES, NumIndices(Portal_Walls.size()), GL_UNSIGNED_BYTE, 0);
glBindVertexArray(0);


And right now the shaders are like so:
/////////Vertex Shader
#version 150

uniform mat4 ProjectionModelviewMatrix;
in vec4 inVertex;
in vec2 inTexCoord0;

out vec2 outTexCoord0;

void main()
{
gl_Position = ProjectionModelviewMatrix * inVertex;
outTexCoord0 = inTexCoord0;
}
/////////////Fragment Shader
#version 150

uniform sampler2D tex;

in vec2 outTexCoord0;

out vec4 outFragColor;

vec4 mycolor;

void main()
{
mycolor = texture2D(tex, outTexCoord0);

outFragColor = mycolor;
}


Screen is blank, no drawing at all.

[Edited by - PrestoChung on December 12, 2010 8:22:58 AM]

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Since I can't use ftransform() I think I am not getting the Projection and Modelview Matrix to my shader properly.

I added this code before linking with:
glLinkProgramARB(Shader_Program)
GLfloat modelview[16]; 
glGetFloatv(GL_MODELVIEW_MATRIX, modelview);
GLfloat projection[16];
glGetFloatv(GL_PROJECTION_MATRIX, projection);
GLuint loc;
GLuint loc2;
loc = glGetUniformLocationARB(Component::Shader_Program,"ModelViewMatrix");
glUniform4fvARB(loc,4,modelview);
loc2 = glGetUniformLocationARB(Component::Shader_Program,"ProjectionMatrix");
glUniform4fvARB(loc2,4,projection);
Now I think I'll have to call some of these functions every frame if the view has changed? This is all a bit new to me as before I just called
gluLookAt()
and never had to touch the matrices directly.

This changes the vert shader to:
#version 150

uniform mat4 ProjectionMatrix;
uniform mat4 ModelviewMatrix;

in vec4 inVertex;
in vec2 inTexCoord0;

out vec2 outTexCoord0;

void main()
{
gl_Position = ProjectionMatrix * ModelviewMatrix * inVertex;
outTexCoord0 = inTexCoord0;
}

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I suggest you upconvert your GL_UNSIGNED_BYTE to GL_UNSIGNED_SHORT. The reason is that I suspect it is not hw accelerated.
This page has the basic problems to avoid. It doesn't list about your case.


http://www.opengl.org/wiki/Common_Mistakes

Your case is here
http://www.opengl.org/wiki/Vertex_Arrays

and at the bottom it says, Use 16 bit integer.
I'll update the Common Mistakes page.

For your
gluLookAt()
glTranslatef()
and all that shit, you can use a library such as my glhlib
http://glhlib.sourceforge.net

but that's Windows 32 bit only.

There are others such as the GLM
and many others over at
http://www.gamedev.net/community/forums/topic.asp?topic_id=339189

My own glhlib looks like GL

float Matrix_3DNoiseTexture[16];
glhLoadIdentityf2(Matrix_3DNoiseTexture);
glhTranslatef2(Matrix_3DNoiseTexture, Translate3DNoiseTexture[0], Translate3DNoiseTexture[1], Translate3DNoiseTexture[2]);
glhRotateAboutZf2(Matrix_3DNoiseTexture, Rotate3DNoiseTexture[2]);
glhRotateAboutYf2(Matrix_3DNoiseTexture, Rotate3DNoiseTexture[1]);
glhRotateAboutXf2(Matrix_3DNoiseTexture, Rotate3DNoiseTexture[0]);
glhScalef2(Matrix_3DNoiseTexture, Scale3DNoiseTexture, Scale3DNoiseTexture, Scale3DNoiseTexture);



All the functions are there. There are also the SSE versions for mass data processing.

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Why would I want to get rid of glLookAt()?

I did change the indices to GLushort s but nothing happens still. They were working before.

Is this what I should call after updating the viewpoint?
CameraUpdate(){
glLoadIdentity();
gluLookAt( Pos_.X(), Pos_.Y(), Pos_.Z(),
Loo_.X(), Loo_.Y(), Loo_.Z(),
Up_.X(), Up_.Y(), Up_.Z() );

GLfloat modelview[16];
glGetFloatv(GL_MODELVIEW_MATRIX, modelview);
GLfloat projection[16];
glGetFloatv(GL_PROJECTION_MATRIX, projection);
GLuint loc;
GLuint loc2;
loc = glGetUniformLocationARB(Component::Shader_Program,"ModelViewMatrix");
glUniform4fvARB(loc,4,modelview);
loc2 = glGetUniformLocationARB(Component::Shader_Program,"ProjectionMatrix");
glUniform4fvARB(loc2,4,projection);
}

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I noticed I have
glEnableClientState( GL_VERTEX_ARRAY );
glEnableClientState( GL_TEXTURE_COORD_ARRAY );
before rendering and
glDisableClientState(GL_VERTEX_ARRAY);
glDisableClientState(GL_TEXTURE_COORD_ARRAY);
after rendering.

Should these be removed if I am trying to use generic vertex attributes?

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One thing I noticed is a glGetError 1280 (invalid enum) that occurs after this line
glGetProgramivARB(Component::Shader_Program, GL_LINK_STATUS, &linked);
This would seem to indicate that GL_LINK_STATUS is not a valid enum for this function. Is there an ARB version of this enum? If so, what is it? GL_LINK_STATUS_ARB seems to be invalid.

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      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 two samples, asteroids performance benchmark and example Unity project that uses Diligent Engine in native plugin.
      AntTweakBar sample is Diligent Engine’s “Hello World” example.

       
      Atmospheric scattering sample is a more advanced example. It 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 and Android platforms. Direct3D11, Direct3D12, OpenGL/GLES backends are now feature complete. Vulkan backend is coming next, and support for more platforms is planned.
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