# OpenGL row major vs.column major

This topic is 2855 days old which is more than the 365 day threshold we allow for new replies. Please post a new topic.

## Recommended Posts

If we send a row major matrix to glMultMatrix() and again get the matrix using glGet() function, we get the same matrix. For example 12th, 13th and 14th elements always consist of translation elements for both row major and column major matrices. But here's a quote from the book "More OpenGL game programming": Also note that the product of the projection matrices is transposed before being passed to glTexGenv(). This is necessary because all three matrices store data in column major order. After transposing, the result is in row major order which is what glTexGenfv() expects. ... The author uses this way to get the projection matrix: gluPerspective( fovy, aspect_ratio, 1, 100 ); glGetFloatv( GL_PROJECTION_MATRIX, ( GLfloat*)&mat4_projection ); But I'm wondering! Both row major and column major matrices store the data the same way. ( m[0], m[1], etc ). But the way that they deal with rows or columns is different. I have seen an Open Source example that simply works with row major matrices and pre multiplies them and then sends the result to glMultMatrix(). I guess that something is going wrong in his article.

##### Share on other sites
But he just gets the result from OpenGL:

gluPerspective( fovy, aspect_ratio, 1, 100 );
glGetFloatv( GL_PROJECTION_MATRIX, ( GLfloat*)&mat4_projection );

So we don't need to transpose it.

OpenGL always store the translation elements in 12ths, 13th and 14th elements:

array[12] = x

array[13] = y

array[14] = z

array[15] = 1

I have tried it, OpenGL uses row major matrices, but the first row is m[0], m[4], m[8] and m[12] for example.

I guess passing the result to glTexGen() is independent of row major and column major matrices( Assuming that we work with row major ordering ).

The second argument of glTexGen() in his example is GL_EYE_PLANE, So I guess that we need to transpose the matrix to send the correct "plane equation" to this function.
You can find his source code here:
http://glbook.gamedev.net/moglgp/code.asp

[Edited by - ehsan2004 on March 28, 2010 8:51:25 AM]

##### Share on other sites
Wavarian, are you sure?

src/mesa/main/matrix.c: * -# 4x4 transformation matrices are stored in memory in column major order.

##### Share on other sites
Quote:
 Original post by toriWavarian, are you sure?src/mesa/main/matrix.c: * -# 4x4 transformation matrices are stored in memory in column major order.

I read some comments from the OpenGL moderator that both row major and column major matrices use the same 1D array.

But the first row of row major matrices are m[0],m[1], m[2] and m[3] and the first row of column major matrices are m[0], m[4], m[8] and m[12]. After computing the matrix mathes( whether we use row major or column major ) , the values of m[0] to m[15] are the same for both matrices ( OpenGL uses post multiplication and DirectX uses Pre multiplication, so we get the same results ).

##### Share on other sites
The quote from that book seems to be out of context. It sounds like the author is manually inverting the matrix before sending it to OpenGL rather than expecting OpenGL to invert it or him. Note that there's no way for OpenGL to know if a matrix (given as a 1D array) is row- or column-major, so there's no way for it to know whether to invert your matrix.

##### Share on other sites
Regardless whether you have a D3D matrix
[  0  1  2  3 ][  4  5  6  7 ][  8  9 10 11 ][ 12 13 14 15 ]
or a OpenGL matrix (the transpose of the above one)
[  0  4  8 12 ][  1  5  9 13 ][  2  6 10 14 ][  3  7 11 15 ]
in linear memory (i.e. from lower address to higher address) the layout is
{ 0, 1, 2, 3, 4, ..., 15 }

This means that you need not re-order to use that for either D3D or OpenGL (but you need to do so for e.g. Collada!) because if you use it in D3D you would do a row vector multiplication
              [  0  1  2  3 ][ x y z w ] * [  4  5  6  7 |              [  8  9 10 11 ]              [ 12 13 14 15 ]
, and in OpenGL a column vector multiplication
[  0  4  8 12 ]   [ x [[  1  5  9 13 ] * [ y ][  2  6 10 14 ]   [ z ][  3  7 11 15 ]   [ w ]
so that the results are identical, aren't they? The quintessence is, that row vectors together with row major order on the one hand, and column vectors together with column major order on the other hand produce the same layout in memory.

Quote:
 Original post by ehsan2004I have seen an Open Source example that simply works with row major matrices and pre multiplies them and then sends the result to glMultMatrix().

Maybe the following mathematical rule was used:
( A * B )T = BT * AT

BTW: Whether the elements 12, 13, 14 store the translation depends additionally on the conventation that the homogeneous co-ordinate is store at the 4th place in a 4D vector. Both D3D as well as OpenGL use this convention, but other APIs/formats may use another one.

##### Share on other sites
But I don't see any matrix inversion there:
	mat4(const mat4 &m) {		mat[0] = m[0]; mat[4] = m[4]; mat[8] = m[8]; mat[12] = m[12];		mat[1] = m[1]; mat[5] = m[5]; mat[9] = m[9]; mat[13] = m[13];		mat[2] = m[2]; mat[6] = m[6]; mat[10] = m[10]; mat[14] = m[14];		mat[3] = m[3]; mat[7] = m[7]; mat[11] = m[11]; mat[15] = m[15];	}

	mat4 operator*(const mat4 &m) const {		mat4 ret;		ret[0] = mat[0] * m[0] + mat[4] * m[1] + mat[8] * m[2] + mat[12] * m[3];		ret[1] = mat[1] * m[0] + mat[5] * m[1] + mat[9] * m[2] + mat[13] * m[3];		ret[2] = mat[2] * m[0] + mat[6] * m[1] + mat[10] * m[2] + mat[14] * m[3];		ret[3] = mat[3] * m[0] + mat[7] * m[1] + mat[11] * m[2] + mat[15] * m[3];		ret[4] = mat[0] * m[4] + mat[4] * m[5] + mat[8] * m[6] + mat[12] * m[7];		ret[5] = mat[1] * m[4] + mat[5] * m[5] + mat[9] * m[6] + mat[13] * m[7];		ret[6] = mat[2] * m[4] + mat[6] * m[5] + mat[10] * m[6] + mat[14] * m[7];		ret[7] = mat[3] * m[4] + mat[7] * m[5] + mat[11] * m[6] + mat[15] * m[7];		ret[8] = mat[0] * m[8] + mat[4] * m[9] + mat[8] * m[10] + mat[12] * m[11];		ret[9] = mat[1] * m[8] + mat[5] * m[9] + mat[9] * m[10] + mat[13] * m[11];		ret[10] = mat[2] * m[8] + mat[6] * m[9] + mat[10] * m[10] + mat[14] * m[11];		ret[11] = mat[3] * m[8] + mat[7] * m[9] + mat[11] * m[10] + mat[15] * m[11];		ret[12] = mat[0] * m[12] + mat[4] * m[13] + mat[8] * m[14] + mat[12] * m[15];		ret[13] = mat[1] * m[12] + mat[5] * m[13] + mat[9] * m[14] + mat[13] * m[15];		ret[14] = mat[2] * m[12] + mat[6] * m[13] + mat[10] * m[14] + mat[14] * m[15];		ret[15] = mat[3] * m[12] + mat[7] * m[13] + mat[11] * m[14] + mat[15] * m[15];		return ret;	}

For example, he has also calculated the texture matrix for the shader( When using shader ), But he has not transposed the results:
void CProjector :: SetupTexMatrix(){	float offset[16] = { 0.5f,	0,	0,	0,				 0,	0.5f,	0,	0, 				 0,		0,	0,	0,				 0.5f,0.5f, 0.0f, 1 };		mat4 m_offset = mat4(offset);	mat4 m_result = m_offset * mat4_projection * mat4_view; 		glMatrixMode(GL_TEXTURE);	glLoadMatrixf((GLfloat*) &m_result);	glMatrixMode(GL_MODELVIEW);}

You can find his source code here:
http://glbook.gamedev.net/moglgp/code.asp

##### Share on other sites
I'm agree with haegarr.

Also note that the product of the projection matrices is transposed before being passed to glTexGenv(). This is necessary because all three matrices store data in column major order. After transposing, the result is in row major order which is what glTexGenfv() expects.
...

I don't agree with the author. I guess It's about passing the correct equation to glTexGen(), It's not about the DirectX or OpenGL matrices.

##### Share on other sites
Quote:
 This means that you need not re-order to use that for either D3D or OpenGL (but you need to do so for e.g. Collada!)

Yes, I don't know why Collada has used that ordering. I also transposed the bind shape matrices because Collada stores the transpose of the standard row major ordering! (For example regarding the Collada spec, translation elements are stored in m[3], m[7] and m[11] !
I remember that someone reported the bug to Collada forum, but we still see the same rule in Collada specification.

##### Share on other sites
Quote:
 Original post by ehsan2004Yes, I don't know why Collada has used that ordering. I also transposed the bind shape matrices because Collada stores the transpose of the standard row major ordering! (For example regarding the Collada spec, translation elements are stored in m[3], m[7] and m[11] !I remember that someone reported the bug to Collada forum, but we still see the same rule in Collada specification.
I'm not sure whether that is really a bug. In fact, you have 2 binary criteria (if neglecting esoteric ones), allowing for 4 combinations:
row vectors and row major order
row vectors and column major order
column vectors and row major order
column vectors and column major order

No one is really superior w.r.t. the others. OpenGL has picked one, D3D another, and Collada a third.

• 10
• 11
• 9
• 16
• 18
• ### Similar Content

• By reenigne
For those that don't know me. I am the individual who's two videos are listed here under setup for https://wiki.libsdl.org/Tutorials
I also run grhmedia.com where I host the projects and code for the tutorials I have online.
Recently, I received a notice from youtube they will be implementing their new policy in protecting video content as of which I won't be monetized till I meat there required number of viewers and views each month.

Frankly, I'm pretty sick of youtube. I put up a video and someone else learns from it and puts up another video and because of the way youtube does their placement they end up with more views.
Even guys that clearly post false information such as one individual who said GLEW 2.0 was broken because he didn't know how to compile it. He in short didn't know how to modify the script he used because he didn't understand make files and how the requirements of the compiler and library changes needed some different flags.

At the end of the month when they implement this I will take down the content and host on my own server purely and it will be a paid system and or patreon.

I get my videos may be a bit dry, I generally figure people are there to learn how to do something and I rather not waste their time.
I used to also help people for free even those coming from the other videos. That won't be the case any more. I used to just take anyone emails and work with them my email is posted on the site.

I don't expect to get the required number of subscribers in that time or increased views. Even if I did well it wouldn't take care of each reoccurring month.
I figure this is simpler and I don't plan on putting some sort of exorbitant fee for a monthly subscription or the like.
I was thinking on the lines of a few dollars 1,2, and 3 and the larger subscription gets you assistance with the content in the tutorials if needed that month.
Maybe another fee if it is related but not directly in the content.
The fees would serve to cut down on the number of people who ask for help and maybe encourage some of the people to actually pay attention to what is said rather than do their own thing. That actually turns out to be 90% of the issues. I spent 6 hours helping one individual last week I must have asked him 20 times did you do exactly like I said in the video even pointed directly to the section. When he finally sent me a copy of the what he entered I knew then and there he had not. I circled it and I pointed out that wasn't what I said to do in the video. I didn't tell him what was wrong and how I knew that way he would go back and actually follow what it said to do. He then reported it worked. Yea, no kidding following directions works. But hey isn't alone and well its part of the learning process.

So the point of this isn't to be a gripe session. I'm just looking for a bit of feed back. Do you think the fees are unreasonable?
Should I keep the youtube channel and do just the fees with patreon or do you think locking the content to my site and require a subscription is an idea.

I'm just looking at the fact it is unrealistic to think youtube/google will actually get stuff right or that youtube viewers will actually bother to start looking for more accurate videos.

• i got error 1282 in my code.
sf::ContextSettings settings; settings.majorVersion = 4; settings.minorVersion = 5; settings.attributeFlags = settings.Core; sf::Window window; window.create(sf::VideoMode(1600, 900), "Texture Unit Rectangle", sf::Style::Close, settings); window.setActive(true); window.setVerticalSyncEnabled(true); glewInit(); GLuint shaderProgram = createShaderProgram("FX/Rectangle.vss", "FX/Rectangle.fss"); float vertex[] = { -0.5f,0.5f,0.0f, 0.0f,0.0f, -0.5f,-0.5f,0.0f, 0.0f,1.0f, 0.5f,0.5f,0.0f, 1.0f,0.0f, 0.5,-0.5f,0.0f, 1.0f,1.0f, }; GLuint indices[] = { 0,1,2, 1,2,3, }; GLuint vao; glGenVertexArrays(1, &vao); glBindVertexArray(vao); GLuint vbo; glGenBuffers(1, &vbo); glBindBuffer(GL_ARRAY_BUFFER, vbo); glBufferData(GL_ARRAY_BUFFER, sizeof(vertex), vertex, GL_STATIC_DRAW); GLuint ebo; glGenBuffers(1, &ebo); glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, ebo); glBufferData(GL_ELEMENT_ARRAY_BUFFER, sizeof(indices), indices,GL_STATIC_DRAW); glVertexAttribPointer(0, 3, GL_FLOAT, false, sizeof(float) * 5, (void*)0); glEnableVertexAttribArray(0); glVertexAttribPointer(1, 2, GL_FLOAT, false, sizeof(float) * 5, (void*)(sizeof(float) * 3)); glEnableVertexAttribArray(1); GLuint texture[2]; glGenTextures(2, texture); glActiveTexture(GL_TEXTURE0); glBindTexture(GL_TEXTURE_2D, texture[0]); glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE); glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE); glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR); glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR); sf::Image* imageOne = new sf::Image; bool isImageOneLoaded = imageOne->loadFromFile("Texture/container.jpg"); if (isImageOneLoaded) { glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, imageOne->getSize().x, imageOne->getSize().y, 0, GL_RGBA, GL_UNSIGNED_BYTE, imageOne->getPixelsPtr()); glGenerateMipmap(GL_TEXTURE_2D); } delete imageOne; glActiveTexture(GL_TEXTURE1); glBindTexture(GL_TEXTURE_2D, texture[1]); glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE); glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE); glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR); glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR); sf::Image* imageTwo = new sf::Image; bool isImageTwoLoaded = imageTwo->loadFromFile("Texture/awesomeface.png"); if (isImageTwoLoaded) { glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, imageTwo->getSize().x, imageTwo->getSize().y, 0, GL_RGBA, GL_UNSIGNED_BYTE, imageTwo->getPixelsPtr()); glGenerateMipmap(GL_TEXTURE_2D); } delete imageTwo; glUniform1i(glGetUniformLocation(shaderProgram, "inTextureOne"), 0); glUniform1i(glGetUniformLocation(shaderProgram, "inTextureTwo"), 1); GLenum error = glGetError(); std::cout << error << std::endl; sf::Event event; bool isRunning = true; while (isRunning) { while (window.pollEvent(event)) { if (event.type == event.Closed) { isRunning = false; } } glClear(GL_COLOR_BUFFER_BIT); if (isImageOneLoaded && isImageTwoLoaded) { glActiveTexture(GL_TEXTURE0); glBindTexture(GL_TEXTURE_2D, texture[0]); glActiveTexture(GL_TEXTURE1); glBindTexture(GL_TEXTURE_2D, texture[1]); glUseProgram(shaderProgram); } glBindVertexArray(vao); glDrawElements(GL_TRIANGLES, 6, GL_UNSIGNED_INT, nullptr); glBindVertexArray(0); window.display(); } glDeleteVertexArrays(1, &vao); glDeleteBuffers(1, &vbo); glDeleteBuffers(1, &ebo); glDeleteProgram(shaderProgram); glDeleteTextures(2,texture); return 0; } and this is the vertex shader
#version 450 core layout(location=0) in vec3 inPos; layout(location=1) in vec2 inTexCoord; out vec2 TexCoord; void main() { gl_Position=vec4(inPos,1.0); TexCoord=inTexCoord; } and the fragment shader
#version 450 core in vec2 TexCoord; uniform sampler2D inTextureOne; uniform sampler2D inTextureTwo; out vec4 FragmentColor; void main() { FragmentColor=mix(texture(inTextureOne,TexCoord),texture(inTextureTwo,TexCoord),0.2); } I was expecting awesomeface.png on top of container.jpg

• By khawk
We've just released all of the source code for the NeHe OpenGL lessons on our Github page at https://github.com/gamedev-net/nehe-opengl. code - 43 total platforms, configurations, and languages are included.
Now operated by GameDev.net, NeHe is located at http://nehe.gamedev.net where it has been a valuable resource for developers wanting to learn OpenGL and graphics programming.

View full story
• By TheChubu
The Khronos™ Group, an open consortium of leading hardware and software companies, announces from the SIGGRAPH 2017 Conference the immediate public availability of the OpenGL® 4.6 specification. OpenGL 4.6 integrates the functionality of numerous ARB and EXT extensions created by Khronos members AMD, Intel, and NVIDIA into core, including the capability to ingest SPIR-V™ shaders.
SPIR-V is a Khronos-defined standard intermediate language for parallel compute and graphics, which enables content creators to simplify their shader authoring and management pipelines while providing significant source shading language flexibility. OpenGL 4.6 adds support for ingesting SPIR-V shaders to the core specification, guaranteeing that SPIR-V shaders will be widely supported by OpenGL implementations.
OpenGL 4.6 adds the functionality of these ARB extensions to OpenGL’s core specification:
GL_ARB_gl_spirv and GL_ARB_spirv_extensions to standardize SPIR-V support for OpenGL GL_ARB_indirect_parameters and GL_ARB_shader_draw_parameters for reducing the CPU overhead associated with rendering batches of geometry GL_ARB_pipeline_statistics_query and GL_ARB_transform_feedback_overflow_querystandardize OpenGL support for features available in Direct3D GL_ARB_texture_filter_anisotropic (based on GL_EXT_texture_filter_anisotropic) brings previously IP encumbered functionality into OpenGL to improve the visual quality of textured scenes GL_ARB_polygon_offset_clamp (based on GL_EXT_polygon_offset_clamp) suppresses a common visual artifact known as a “light leak” associated with rendering shadows GL_ARB_shader_atomic_counter_ops and GL_ARB_shader_group_vote add shader intrinsics supported by all desktop vendors to improve functionality and performance GL_KHR_no_error reduces driver overhead by allowing the application to indicate that it expects error-free operation so errors need not be generated In addition to the above features being added to OpenGL 4.6, the following are being released as extensions:
GL_KHR_parallel_shader_compile allows applications to launch multiple shader compile threads to improve shader compile throughput WGL_ARB_create_context_no_error and GXL_ARB_create_context_no_error allow no error contexts to be created with WGL or GLX that support the GL_KHR_no_error extension “I’m proud to announce OpenGL 4.6 as the most feature-rich version of OpenGL yet. We've brought together the most popular, widely-supported extensions into a new core specification to give OpenGL developers and end users an improved baseline feature set. This includes resolving previous intellectual property roadblocks to bringing anisotropic texture filtering and polygon offset clamping into the core specification to enable widespread implementation and usage,” said Piers Daniell, chair of the OpenGL Working Group at Khronos. “The OpenGL working group will continue to respond to market needs and work with GPU vendors to ensure OpenGL remains a viable and evolving graphics API for all its customers and users across many vital industries.“
The OpenGL 4.6 specification can be found at https://khronos.org/registry/OpenGL/index_gl.php. The GLSL to SPIR-V compiler glslang has been updated with GLSL 4.60 support, and can be found at https://github.com/KhronosGroup/glslang.
Sophisticated graphics applications will also benefit from a set of newly released extensions for both OpenGL and OpenGL ES to enable interoperability with Vulkan and Direct3D. These extensions are named:
GL_EXT_memory_object GL_EXT_memory_object_fd GL_EXT_memory_object_win32 GL_EXT_semaphore GL_EXT_semaphore_fd GL_EXT_semaphore_win32 GL_EXT_win32_keyed_mutex They can be found at: https://khronos.org/registry/OpenGL/index_gl.php
Industry Support for OpenGL 4.6
“With OpenGL 4.6 our customers have an improved set of core features available on our full range of OpenGL 4.x capable GPUs. These features provide improved rendering quality, performance and functionality. As the graphics industry’s most popular API, we fully support OpenGL and will continue to work closely with the Khronos Group on the development of new OpenGL specifications and extensions for our customers. NVIDIA has released beta OpenGL 4.6 drivers today at https://developer.nvidia.com/opengl-driver so developers can use these new features right away,” said Bob Pette, vice president, Professional Graphics at NVIDIA.
"OpenGL 4.6 will be the first OpenGL release where conformant open source implementations based on the Mesa project will be deliverable in a reasonable timeframe after release. The open sourcing of the OpenGL conformance test suite and ongoing work between Khronos and X.org will also allow for non-vendor led open source implementations to achieve conformance in the near future," said David Airlie, senior principal engineer at Red Hat, and developer on Mesa/X.org projects.

View full story
• By _OskaR
Hi,
I have an OpenGL application but without possibility to wite own shaders.
I need to perform small VS modification - is possible to do it in an alternative way? Do we have apps or driver modifictions which will catch the shader sent to GPU and override it?