• Advertisement

# OpenGL GL_MODELVIEW matrix confusion

This topic is 3632 days old which is more than the 365 day threshold we allow for new replies. Please post a new topic.

If you intended to correct an error in the post then please contact us.

## Recommended Posts

Hi, I have some experience with Direct3D, but I'm new to OpenGL. I'm having problems drawing a cube at an arbitrary location in the world. I managed to get things working using gluLookAt, but I'd prefer to create the view matrix myself then multiply it by the current objects world matrix e.g. glLoadMatrixd( camera.viewMatrix() * object.worldMatrix() ); So, the current setup is the object is located at the origin, with: right vector = <1, 0, 0> up vector = <0, 1, 0> look vector = <0, 0, -1> The camera is located at <0, 0, 10>. Its right, up, and look vectors are identical to the object (I'm not doing any rotations at the moment). The view matrix created by Camera::viewMatrix is:
"[         1,          0,          0,          0]
[         0,          1,          0,          0]
[         0,          0,         -1,        -10]
[         0,          0,          0,          1]"


const GLdouble* Camera_Class::View_Matrix(void)
{
if (m_View_Matrix_Dirty == false)
{
return m_View_Matrix;
}

// Row 1
m_View_Matrix[0] = m_Right_Vector[0];
m_View_Matrix[1] = m_Right_Vector[1];
m_View_Matrix[2] = m_Right_Vector[2];
m_View_Matrix[3] = -1.0 * (m_Position_Vector * m_Right_Vector);
// Row 2
m_View_Matrix[4] = m_Up_Vector[0];
m_View_Matrix[5] = m_Up_Vector[1];
m_View_Matrix[6] = m_Up_Vector[2];
m_View_Matrix[7] = -1.0 * (m_Position_Vector * m_Up_Vector);
// Row 3
m_View_Matrix[8] = m_Look_Vector[0];
m_View_Matrix[9] = m_Look_Vector[1];
m_View_Matrix[10] = m_Look_Vector[2];
m_View_Matrix[11] = -1.0 * (m_Position_Vector * m_Look_Vector);
// Row 4
m_View_Matrix[12] = 0.0;
m_View_Matrix[13] = 0.0;
m_View_Matrix[14] = 0.0;
m_View_Matrix[15] = 1.0;

m_View_Matrix_Dirty = false;

return m_View_Matrix;
}


Here is the paint function:
void OpenGL_Widget_Class::paintGL(void)
{
glClear(GL_COLOR_BUFFER_BIT);

glLoadMatrixd(m_Camera.View_Matrix());

glEnableClientState(GL_VERTEX_ARRAY);
glEnableClientState(GL_COLOR_ARRAY);
glEnableClientState(GL_INDEX_ARRAY);

glVertexPointer(3, GL_DOUBLE, 0, m_Vertices);
glColorPointer(4, GL_DOUBLE, 0, m_Colors);
glIndexPointer(GL_INT, 0, m_Indices);

// Row major
// world_matrix = yaw * pitch * roll * world_matrix

// Column major
// world_matrix = ((world_matrix * roll) * pitch) * yaw

for(QList<Object_Class*>::iterator iter = m_Cube_Objects.begin(); iter != m_Cube_Objects.end(); ++iter)
{
glDrawElements(GL_QUADS, 24, GL_UNSIGNED_INT, m_Indices);
}

glFlush();
}


Other info: the near and far planes are set to 1 and 1000. Many thanks,

#### Share this post

##### Share on other sites
Advertisement
Ok some notes/tips:

GL stores things in column order your matrix should be:

[1, 0, 0, 0,
0, 1, 0, 0,
0, 0, -1, 0,
0, 0, 10, 1 ]

then try:

glMatrixMode(GL_MODELVIEW);
glLoadMatrixd(object); //object/camera may need to be switched, not sure cuz I
glMultMatrixd(camera); //never use LoadMatrix

You should let GL do things, because it's an API that does things uniformly and you don't have to worry about things like column order.

Make sure to use glMatrixMode(GL_MODELVIEW)

#### Share this post

##### Share on other sites
Hi,

Thanks for the tips.

Re your comments about the view matrix, according to my math book, if you are using column vectors, e.g. v' = m*v, then the view matrix should look like:

/*		right_x,	right_y,	right_z,	-(position dot right)		up_x,		up_y,		look_z,		-(position dot up)			look_x,		up_y,		look_z,		-(position dot look)				0,			0,			0,			1		*/

I also understand that i (row index), j (column index) refers to the jth row and ith column in an OpenGL matrix. Keeping both these things in mind, I rewrote my View_Matrix function:

const GLdouble* Camera_Class::View_Matrix(void){	/*	Regular matrix	0, 1, 2, 3,	4, 5, 6, 7,	8, 9, 10, 11,	12, 13, 14, 15	OpenGL matrix	0, 4, 8, 12,	1, 5, 9, 13,	2, 6, 10, 14,	3, 7, 11, 15,	The first row of the matrix occupies elements 0, 4, 8, 12 - not 0, 1, 2, 3		*/	if (m_View_Matrix_Dirty == false) 	{		return m_View_Matrix;	}	// First row of OpenGL matrix	m_View_Matrix[0] = m_Right_Vector[0];	m_View_Matrix[4] = m_Right_Vector[1];	m_View_Matrix[8] = m_Right_Vector[2];	m_View_Matrix[12] = -1 * (m_Position_Vector * m_Right_Vector);	// Second row of OpenGL matrix	m_View_Matrix[1] = m_Up_Vector[0];	m_View_Matrix[5] = m_Up_Vector[1];	m_View_Matrix[9] = m_Up_Vector[2];	m_View_Matrix[13] = -1 * (m_Position_Vector * m_Up_Vector);	// Third row of OpenGL matrix	m_View_Matrix[2] = m_Look_Vector[0];	m_View_Matrix[6] = m_Look_Vector[1];	m_View_Matrix[10] = m_Look_Vector[2];	m_View_Matrix[14] = -1 * (m_Position_Vector * m_Look_Vector);	// Fourth row of OpenGL matrix	m_View_Matrix[3] = 0.0;	m_View_Matrix[7] = 0.0;	m_View_Matrix[11] = 0.0;	m_View_Matrix[15] = 1.0;	m_View_Matrix_Dirty = false;	return m_View_Matrix;}

If the camera is positioned at the origin, this produces a view matrix that is an identity matrix.

[         1,          0,          0,          0][         0,          1,          0,          0][         0,          0,          -1,          0][         0,          0,          0,          1]

My object is positioned 4 units in front of the camera. Its world matrix is:

[         1,          0,          0,          0][         0,          1,          0,          0][         0,          0,          1,          -4][         0,          0,          0,          1]

In the paint function, I multiply the view matrix by the world matrix, then paint the object (a 2x2 cube).

e.g. Result_Matrix = View_Matrix * World_Matrix

The result is a black screen.

Setting the objects position to 4 made the cube visible.

This is a bit confusing because I understood that in OpenGL the +z-axis extends "out of the screen", and the -z-axis into the screen. To move an object in the direction of the world z-axis I'd normally do something like (<0, 0, -1> * distance) + object_position, but that does not work in this case, or my view matrix is still wrong :(

Anyway,

Thanks again

#### Share this post

##### Share on other sites
Your identity matrix has a -1 for the z-axis, so its not the identity..... In any system regardless of the z+ direction, the identity is still all 1's......

So there forefore, you had to switch your translation to this "new system" where you flipped the z-axis.

#### Share this post

##### Share on other sites
Quote:
 Original post by dpadam450GL stores things in column order your matrix should be:
Thats actually not quite true...

Quote:
 Column-major versus row-major is purely a notational convention. Note that post-multiplying with column-major matrices produces the same result as pre-multiplying with row-major matrices. The OpenGL Specification and the OpenGL Reference Manual both use column-major notation. You can use any notation, as long as it's clearly stated.Sadly, the use of column-major format in the spec and blue book has resulted in endless confusion in the OpenGL programming community. Column-major notation suggests that matrices are not laid out in memory as a programmer would expect.

#### Share this post

##### Share on other sites
Yea I've never heard of that, but that doesn't make sense because you cant have both unless there is an option to say "hey I want them row major now". I see what its saying but anytime you print a GL matrix, its always column major, even in GLSL. So can you tell GL how you want it?

#### Share this post

##### Share on other sites
Quote:
 Original post by dpadam450Your identity matrix has a -1 for the z-axis, so its not the identity..... In any system regardless of the z+ direction, the identity is still all 1's......So there forefore, you had to switch your translation to this "new system" where you flipped the z-axis.

Hi,

OK - I set my camera's look vector to <0, 0, 1>, the camera's position to <0, 0, 1>, and the cubes position to <0, 0, -2>.

If +z coordinates are behind the origin, and -z coordinates are in front of the origin, I can visualise this in my head, but the camera's look vector is pointing away from the cube - not at it.

In D3D, if the camera's look vector is <0, 0, 1>, then (a) <0, 0, 10> is a point in front of the origin, and (b) <0, 0, -10> is a point behind the origin.

<0, 0, 0> + (camera_look_vector * 10) = <0, 0, 10> (a).

I would expect things to work the same in OpenGL i.e.

Look vector = <0, 0, -1>
a = <0, 0, -10> // in front of the origin
b = <0, 0, 10> // behind the origin

<0, 0, 0> + (camera_look_vector * 10) = <0, 0, -10> (a)

Do you see what I'm getting at? I'm just trying to get this sorted in my head.

Thanks

#### Share this post

##### Share on other sites
Ok your having coordinate problems un-related to openGL.

Image your origin is the middle of your screen. If your look vector is 0,0,1, then your looking down the positive z-axis, or outward from your pc screen. Your only going to see things that have a positive z-coordinate....

Again, you have this z- concept because your saying "OpenGL's z+ is DX's z-", which is true.......IFFFFF you want to describe GL in terms of DX.

So give this frame if your camera matrix is the identity matrix and remember the z- is the vector into the screen, then anything you see needs to be in the z- axis.

Got it? Again, in your case here, your camera is looking out towards your face, and your cube is behind your pc screen..... complete opposite directions.

OpenGL frame y | | |______ x / /z 
 0 
 Share this post Link to post Share on other sites 
 
 
 davidr    122 davidr    122 Member Member 122 15 posts Joined November 2004 Posted February 22, 2008 Quote:Original post by dpadam450Ok your having coordinate problems un-related to openGL.Image your origin is the middle of your screen. If your look vector is 0,0,1, then your looking down the positive z-axis, or outward from your pc screen. Your only going to see things that have a positive z-coordinate....Again, you have this z- concept because your saying "OpenGL's z+ is DX's z-", which is true.......IFFFFF you want to describe GL in terms of DX.So give this frame if your camera matrix is the identity matrix and remember the z- is the vector into the screen, then anything you see needs to be in the z- axis. Got it? Again, in your case here, your camera is looking out towards your face, and your cube is behind your pc screen..... complete opposite directions.OpenGL frame y | | |______ x / /zThanks for the clarification.In view space, the camera's vectors are aligned with <1, 0, 0>, <0, 1, 0>, and <0, 0, 1>, and objects need to have a position such as <x, y, -z> in order to be visible because OpenGL uses a right-handed coordinate system.Anyway, things seem to be working now. 0 Share this post Link to post Share on other sites songuke    122 songuke    122 Member Member 122 10 posts Joined November 2007 Posted March 13, 2008 /* transform matrix */ Vector3f n = view - eye; //look Vector3f u = n.Cross(up); //right //Vector3f v = n.Cross(u); //left-handed - ??? Vector3f v = u.Cross(n); //right-handed - currently I used this u = u.Normalize(); v = v.Normalize(); n = n.Normalize(); /* make n as -z (negative z) in OpenGL (we look to the negative OpenGL) */ n = -n; //now become left-handed //translation Vector3f t = Vector3f(-eye.Dot(u), -eye.Dot(v), -eye.Dot(n)); /* interpreting as column-major like this in OpenGL * ( u.x, u.y, u.z, t.x, * v.x, v.y, v.z, t.y, * n.x, n.y, n.z, t.z, * 0 , 0, 0, 1 ) */ GLfloat m[] = { //so the matrix must be like this: u.x, v.x, n.x, 0, u.y, v.y, n.y, 0, u.z, v.z, n.z, 0, t.x, t.y, t.z, 1 };I tested this transformation and gained the same result as gluLookAt method.But now I'm having a problem deriving this for the billboard. The billboard code is like this: Vector3f n = vecView; //vector from object of billboard to camera Vector3f u = vecUp.Cross(n); /* !!! Point to the left??? */ Vector3f v = n.Cross(u); u = u.Normalize(); v = v.Normalize(); n = n.Normalize(); //no translation yet //Vector3f t = Vector3f(-posObj.Dot(u), -posObj.Dot(v), -posObj.Dot(n)); /* interpreting as column-major like this * ( u.x, u.y, u.z, t.x, * v.x, v.y, v.z, t.y, * n.x, n.y, n.z, t.z, * 0 , 0, 0, 1 ) */ /* THIS ONE NOT WORK!!! GLfloat m[] = { u.x, v.x, n.x, 0, u.y, v.y, n.y, 0, u.z, v.z, n.z, 0, t.x, t.y, t.z, 1 };*/ /*BUT THIS ONE WORKS!!! -> This matrix's rotation part (u, v, n) is wrong of its position.*/ GLfloat billboardMat[] = { u.x, u.y, u.z, 0, v.x, v.y, v.z, 0, n.x, n.y, n.z, 0, t.x, t.y, t.z, 1 };The billboard matrix is like this. I thought the billboardMat's elements is wrong but it does produce the right result of billboard.In the opposite, if I used the camera transformation matrix without the line n = -n, I still get the billboard effect but the rotation of Y axis is wrong (the image is upside down).It looks confusing. Anyone could give me some hints? :)Thanks in advance. 0 Share this post Link to post Share on other sites V-man    813 V-man    813 Contributor Member 813 4323 posts Joined March 2002 Posted March 14, 2008 You don't need to callglEnableClientState(GL_INDEX_ARRAY);That is for color index. It has nothing to do with indices. 0 Share this post Link to post Share on other sites 
 Sign in to follow this   Followers 0 
 Go To Topic Listing Graphics and GPU Programming Advertisement 
 Advertisement Popular Tags 2D 3D Advice Algorithm C# C++ Character Concept Design DX11 Feedback GameMaker Gameplay General Java Learning Mobile Music OpenGL PC Pixel Python Unity Unreal VR Advertisement Popular Now 10 Upvoting and Downvoting By francoisdiy Started Yesterday at 04:48 PM 14 Breaking into the Industry with a Bad Degree - Can it be Done? By rcrawford115 Started Tuesday at 03:57 PM 11 The fun of the last part of playing RTS By Pleistorm Started Tuesday at 01:12 PM 10 DX11 Duplicate Vertices using std::map By isu diss Started Tuesday at 08:11 AM 11 Need to map Xbox360 controller. By Timothy Sharp Started Tuesday at 12:31 AM Similar Content GLX context creation for an existing window? By Finalspace I am starting to get into linux X11/GLX programming, but from every C example i found - there is this XVisualInfo thing parameter passed to XCreateWindow always. Can i control this parameter later on - when the window is already created? What i want it to change my own non GLX window to be a GLX window - without recreating. Is that possible?   On win32 this works just fine to create a rendering context later on, i simply find and setup the pixel format from a pixel format descriptor and create the context and are ready to go.   I am asking, because if that doesent work - i need to change a few things to support both worlds (Create a context from a existing window, create a context for a new window). Designing A Modern Cross-Platform Graphics Library By DiligentDev This article uses material originally posted on Diligent Graphics web site. Introduction Graphics APIs have come a long way from small set of basic commands allowing limited control of configurable stages of early 3D accelerators to very low-level programming interfaces exposing almost every aspect of the underlying graphics hardware. Next-generation APIs, Direct3D12 by Microsoft and Vulkan by Khronos are relatively new and have only started getting widespread adoption and support from hardware vendors, while Direct3D11 and OpenGL are still considered industry standard. New APIs can provide substantial performance and functional improvements, but may not be supported by older hardware. An application targeting wide range of platforms needs to support Direct3D11 and OpenGL. New APIs will not give any advantage when used with old paradigms. It is totally possible to add Direct3D12 support to an existing renderer by implementing Direct3D11 interface through Direct3D12, but this will give zero benefits. Instead, new approaches and rendering architectures that leverage flexibility provided by the next-generation APIs are expected to be developed. There are at least four APIs (Direct3D11, Direct3D12, OpenGL/GLES, Vulkan, plus Apple's Metal for iOS and osX platforms) that a cross-platform 3D application may need to support. Writing separate code paths for all APIs is clearly not an option for any real-world application and the need for a cross-platform graphics abstraction layer is evident. The following is the list of requirements that I believe such layer needs to satisfy: Lightweight abstractions: the API should be as close to the underlying native APIs as possible to allow an application leverage all available low-level functionality. In many cases this requirement is difficult to achieve because specific features exposed by different APIs may vary considerably. Low performance overhead: the abstraction layer needs to be efficient from performance point of view. If it introduces considerable amount of overhead, there is no point in using it. Convenience: the API needs to be convenient to use. It needs to assist developers in achieving their goals not limiting their control of the graphics hardware. Multithreading: ability to efficiently parallelize work is in the core of Direct3D12 and Vulkan and one of the main selling points of the new APIs. Support for multithreading in a cross-platform layer is a must. Extensibility: no matter how well the API is designed, it still introduces some level of abstraction. In some cases the most efficient way to implement certain functionality is to directly use native API. The abstraction layer needs to provide seamless interoperability with the underlying native APIs to provide a way for the app to add features that may be missing. Diligent Engine is designed to solve these problems. Its main goal is to take advantages of the next-generation APIs such as Direct3D12 and Vulkan, but at the same time provide support for older platforms via Direct3D11, OpenGL and OpenGLES. Diligent Engine exposes common C++ front-end for all supported platforms and provides interoperability with underlying native APIs. It also supports integration with Unity and is designed to be used as graphics subsystem in a standalone game engine, Unity native plugin or any other 3D application. Full source code is available for download at GitHub and is free to use. Overview Diligent Engine API takes some features from Direct3D11 and Direct3D12 as well as introduces new concepts to hide certain platform-specific details and make the system easy to use. It contains the following main components: Render device (IRenderDevice  interface) is responsible for creating all other objects (textures, buffers, shaders, pipeline states, etc.). Device context (IDeviceContext interface) is the main interface for recording rendering commands. Similar to Direct3D11, there are immediate context and deferred contexts (which in Direct3D11 implementation map directly to the corresponding context types). Immediate context combines command queue and command list recording functionality. It records commands and submits the command list for execution when it contains sufficient number of commands. Deferred contexts are designed to only record command lists that can be submitted for execution through the immediate context. An alternative way to design the API would be to expose command queue and command lists directly. This approach however does not map well to Direct3D11 and OpenGL. Besides, some functionality (such as dynamic descriptor allocation) can be much more efficiently implemented when it is known that a command list is recorded by a certain deferred context from some thread. The approach taken in the engine does not limit scalability as the application is expected to create one deferred context per thread, and internally every deferred context records a command list in lock-free fashion. At the same time this approach maps well to older APIs. In current implementation, only one immediate context that uses default graphics command queue is created. To support multiple GPUs or multiple command queue types (compute, copy, etc.), it is natural to have one immediate contexts per queue. Cross-context synchronization utilities will be necessary. Swap Chain (ISwapChain interface). Swap chain interface represents a chain of back buffers and is responsible for showing the final rendered image on the screen. Render device, device contexts and swap chain are created during the engine initialization. Resources (ITexture and IBuffer interfaces). There are two types of resources - textures and buffers. There are many different texture types (2D textures, 3D textures, texture array, cubmepas, etc.) that can all be represented by ITexture interface. Resources Views (ITextureView and IBufferView interfaces). While textures and buffers are mere data containers, texture views and buffer views describe how the data should be interpreted. For instance, a 2D texture can be used as a render target for rendering commands or as a shader resource. Pipeline State (IPipelineState interface). GPU pipeline contains many configurable stages (depth-stencil, rasterizer and blend states, different shader stage, etc.). Direct3D11 uses coarse-grain objects to set all stage parameters at once (for instance, a rasterizer object encompasses all rasterizer attributes), while OpenGL contains myriad functions to fine-grain control every individual attribute of every stage. Both methods do not map very well to modern graphics hardware that combines all states into one monolithic state under the hood. Direct3D12 directly exposes pipeline state object in the API, and Diligent Engine uses the same approach. Shader Resource Binding (IShaderResourceBinding interface). Shaders are programs that run on the GPU. Shaders may access various resources (textures and buffers), and setting correspondence between shader variables and actual resources is called resource binding. Resource binding implementation varies considerably between different API. Diligent Engine introduces a new object called shader resource binding that encompasses all resources needed by all shaders in a certain pipeline state. API Basics Creating Resources 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. Handle Debug Draws 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 A batch of opengl questions 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 Modern OpenGL GLSL Camera 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   Advertisement GDNet Discord Chat All Activity Home Forums Programming Graphics and GPU Programming GL_MODELVIEW matrix confusion