Followers 0

# OpenGL WebGL - How to send an array of matrices to the vertex shader?

## 8 posts in this topic

I want to send an array of matrices (to be more specific: a dynamically changing between draw calls Float32Array of 4x4 Float32Arrays) to a vertex shader with multiple model matrices (size of this.modelMatrices depends on how many objects are moving, so there may be only one model matrix and just in the next frame there may be 30 of them).

When I just call:
gl.uniformMatrix4fv(program.mMatrixUniform, false, this.modelMatrices);
where this.modelMatrices is an Float32Array, and program.mMatrixUniform is declared like this:
program.mMatrixUniform = gl.getUniformLocation(program, 'uMMatrix');
it throws:
gl.INVALID_VALUE was caused by call to: uniformMatrix4fv.

In OpenGL uniformMatrix4fv there is an additional count attribute, which allows to specify the amount of matrices sent while in WebGL there isn't. Also, the question is, does dynamically changing this.modelMatrices causes a problem too?

What is a proper way of doing it in WebGL?
0

##### Share on other sites

depends on how many objects are moving, so there may be only one model matrix and just in the next frame there may be 30 of them).

You need to define in shader the static length of the uniform array of matricies, and since that, the array of floats you pass to uniform setting function cannot be shorter than that (but can be longer since some updates). There is also inablitity to specify offset in the array, so it will always fill the uniform from the begining of array (this is so silly its hard to believe, but I just cannot find the offset accepting functions in specs!)

But there are more ways to set matricies to shaders, you can simply create a vec4 array, and set that, and use it to construct the matricies or just use them as rows the raw way in shader, doting 4d vectors with them.

0

##### Share on other sites

@JohnnyCode

I like the second method, but I'm not sure what would be more computational expensive - creating matrices from an array of vec4 on GPU or sending on each draw call filled Float32Array with let's say 32 matrices? Also I don't need to offset anything since I found a clever way of managing model matrices, so it is not a problem for now.

0

##### Share on other sites

I don't remember if I succeeded in sending Matrix4 arrays.

My engine is sending Vec4 arrays for now.

The reason behind this is that Transformation matrix can be 3x4 which spare you 1 Vec4 per matrix.

Considering you have a limit of uniforms in the vertex shader, this is mostly welcome!

0

##### Share on other sites

In your shader code you need to create the array of elements you want to use

uniform mat4[4] uMMatrix;


In reality, webgl just created four seperate uniforms with the names uMMatrix[0], uMMatrix[1], uMMatrix[2],and uMMatrix[3]. You need to bind them seperately.

program.mMatrixUniform[0] = gl.getUniformLocation(program, 'uMMatrix[0]');
gl.uniformMatrix4fv(program.mMatrixUniform[0], false, this.modelMatrices[0]);

There is more discussion on the subject here

1

##### Share on other sites

Sending an array of floats and saving uniform vectors slots sounds more promising to me than sending ready matrices and binding every one of them separately, so I think I'd rather go that way.

BTW Is there a way to define size of an array in the vertex shader basing on MAX_VERTEX_UNIFORM_VECTORS value, so it would be more 'cross-hardware'?

0

##### Share on other sites

BTW Is there a way to define size of an array in the vertex shader basing on MAX_VERTEX_UNIFORM_VECTORS value, so it would be more 'cross-hardware'?

I would like to correct you here that you should establish as many vectors in a compiled shader as you need, not a single bit more.

If amount you expect shrinks or grows it will bogus up your API calls. (no count or offset parameters in webgl specs uniform setters)

So establish as many vec4a as you need, not more, and check with gl.getParameter(gl.MAX_VERTEX_UNIFORM_VECTORS)) to see if the current setup actualy even supports you least needed amount. If the MVUV provided in outer API of yours is smaller than your needs, you need to fallback on your own responsibility and pick lesser shaders - if even.

0

##### Share on other sites

@JohnnyCode

I'm a little bit confused now.

GLSL specification states - "If an array is indexed with an expression that is not an integral constant expression, or if an array is passed as an argument to a function, then its size must be declared before any such use."

So unless I'd make a long long if-else ladder (which is strongly dissuaded on older GLSL) which would look like this:

else if (matrixIndex == 1)
return mat4(rawMatrices[12], rawMatrices[13], ..., rawMatrices[23], 0, 0, 0, 1);
else if (matrixIndex == 2)
return mat4(rawMatrices[24], rawMatrices[25], ..., rawMatrices[35], 0, 0, 0, 1);
...
else if (matrixIndex == 63)
return mat4(rawMatrices[756], rawMatrices[757], ..., rawMatrices[767], 0, 0, 0, 1); 

I'm bound to declare it's size first, and because of this I can't really see any advantageous solution which would establish as many floats as I need (because of the fact that the amount of needed floats would dynamically change at the runtime).

Edited by Winged
0

##### Share on other sites

(because of the fact that the amount of needed floats would dynamically change at the runtime).

Ah I see what you ment. You want to maximize the array , as much as it can get.

Well if you want to declare an array size of unifrom declaration of a shader to be maximal on a system, you may call gl.getParameter(gl.MAX_VERTEX_UNIFORM_VECTORS)) and put this value to your shader code string, before you compile it (and also knowinng this value for your very aplication) .

Wheather this constant (MAX_VERTEX_UNIFORM_VECTORS) is available in GLSL code compiler I do not know .

But bare in mind that once shader gets compiled, the uniform array keeps its size, so change at the runtime will not be possible unless you recompile, but I do not see why would someone need to change an unifrom array length through runtime? (just fill the unsed rest always,  even bogus,  you cannot specify count in webgl so always pass conforming array of floats)

You can index vec4 array with an expresion in vertex shader I am sure.

like :

uniform vec4 u_vecs[256];

....

int ind = 6 ; // sixth matrix

mat4 themat=mat4(u_vecs[ind*4],u_vecs[ind*4+1],u_vecs[ind*4+2],u_vecs[ind*4+3]);

0

## Create an account

Register a new account

Followers 0

• ### Similar Content

• By mapra99
Hello

I am working on a recent project and I have been learning how to code in C# using OpenGL libraries for some graphics. I have achieved some quite interesting things using TAO Framework writing in Console Applications, creating a GLUT Window. But my problem now is that I need to incorporate the Graphics in a Windows Form so I can relate the objects that I render with some .NET Controls.

To deal with this problem, I have seen in some forums that it's better to use OpenTK instead of TAO Framework, so I can use the glControl that OpenTK libraries offer. However, I haven't found complete articles, tutorials or source codes that help using the glControl or that may insert me into de OpenTK functions. Would somebody please share in this forum some links or files where I can find good documentation about this topic? Or may I use another library different of OpenTK?

Thanks!

• Hello, I have been working on SH Irradiance map rendering, and I have been using a GLSL pixel shader to render SH irradiance to 2D irradiance maps for my static objects. I already have it working with 9 3D textures so far for the first 9 SH functions.
In my GLSL shader, I have to send in 9 SH Coefficient 3D Texures that use RGBA8 as a pixel format. RGB being used for the coefficients for red, green, and blue, and the A for checking if the voxel is in use (for the 3D texture solidification shader to prevent bleeding).
My problem is, I want to knock this number of textures down to something like 4 or 5. Getting even lower would be a godsend. This is because I eventually plan on adding more SH Coefficient 3D Textures for other parts of the game map (such as inside rooms, as opposed to the outside), to circumvent irradiance probe bleeding between rooms separated by walls. I don't want to reach the 32 texture limit too soon. Also, I figure that it would be a LOT faster.
Is there a way I could, say, store 2 sets of SH Coefficients for 2 SH functions inside a texture with RGBA16 pixels? If so, how would I extract them from inside GLSL? Let me know if you have any suggestions ^^.
• By KarimIO
EDIT: I thought this was restricted to Attribute-Created GL contexts, but it isn't, so I rewrote the post.
Hey guys, whenever I call SwapBuffers(hDC), I get a crash, and I get a "Too many posts were made to a semaphore." from Windows as I call SwapBuffers. What could be the cause of this?
Update: No crash occurs if I don't draw, just clear and swap.
static PIXELFORMATDESCRIPTOR pfd = // pfd Tells Windows How We Want Things To Be { sizeof(PIXELFORMATDESCRIPTOR), // Size Of This Pixel Format Descriptor 1, // Version Number PFD_DRAW_TO_WINDOW | // Format Must Support Window PFD_SUPPORT_OPENGL | // Format Must Support OpenGL PFD_DOUBLEBUFFER, // Must Support Double Buffering PFD_TYPE_RGBA, // Request An RGBA Format 32, // Select Our Color Depth 0, 0, 0, 0, 0, 0, // Color Bits Ignored 0, // No Alpha Buffer 0, // Shift Bit Ignored 0, // No Accumulation Buffer 0, 0, 0, 0, // Accumulation Bits Ignored 24, // 24Bit Z-Buffer (Depth Buffer) 0, // No Stencil Buffer 0, // No Auxiliary Buffer PFD_MAIN_PLANE, // Main Drawing Layer 0, // Reserved 0, 0, 0 // Layer Masks Ignored }; if (!(hDC = GetDC(windowHandle))) return false; unsigned int PixelFormat; if (!(PixelFormat = ChoosePixelFormat(hDC, &pfd))) return false; if (!SetPixelFormat(hDC, PixelFormat, &pfd)) return false; hRC = wglCreateContext(hDC); if (!hRC) { std::cout << "wglCreateContext Failed!\n"; return false; } if (wglMakeCurrent(hDC, hRC) == NULL) { std::cout << "Make Context Current Second Failed!\n"; return false; } ... // OGL Buffer Initialization glClear(GL_DEPTH_BUFFER_BIT | GL_COLOR_BUFFER_BIT); glBindVertexArray(vao); glUseProgram(myprogram); glDrawElements(GL_TRIANGLES, indexCount, GL_UNSIGNED_SHORT, (void *)indexStart); SwapBuffers(GetDC(window_handle));
• By Tchom
Hey devs!

I've been working on a OpenGL ES 2.0 android engine and I have begun implementing some simple (point) lighting. I had something fairly simple working, so I tried to get fancy and added color-tinting light. And it works great... with only one or two lights. Any more than that, the application drops about 15 frames per light added (my ideal is at least 4 or 5). I know implementing lighting is expensive, I just didn't think it was that expensive. I'm fairly new to the world of OpenGL and GLSL, so there is a good chance I've written some crappy shader code. If anyone had any feedback or tips on how I can optimize this code, please let me know.

uniform mat4 u_MVPMatrix; uniform mat4 u_MVMatrix; attribute vec4 a_Position; attribute vec3 a_Normal; attribute vec2 a_TexCoordinate; varying vec3 v_Position; varying vec3 v_Normal; varying vec2 v_TexCoordinate; void main() { v_Position = vec3(u_MVMatrix * a_Position); v_TexCoordinate = a_TexCoordinate; v_Normal = vec3(u_MVMatrix * vec4(a_Normal, 0.0)); gl_Position = u_MVPMatrix * a_Position; } Fragment Shader
precision mediump float; uniform vec4 u_LightPos["+numLights+"]; uniform vec4 u_LightColours["+numLights+"]; uniform float u_LightPower["+numLights+"]; uniform sampler2D u_Texture; varying vec3 v_Position; varying vec3 v_Normal; varying vec2 v_TexCoordinate; void main() { gl_FragColor = (texture2D(u_Texture, v_TexCoordinate)); float diffuse = 0.0; vec4 colourSum = vec4(1.0); for (int i = 0; i < "+numLights+"; i++) { vec3 toPointLight = vec3(u_LightPos[i]); float distance = length(toPointLight - v_Position); vec3 lightVector = normalize(toPointLight - v_Position); float diffuseDiff = 0.0; // The diffuse difference contributed from current light diffuseDiff = max(dot(v_Normal, lightVector), 0.0); diffuseDiff = diffuseDiff * (1.0 / (1.0 + ((1.0-u_LightPower[i])* distance * distance))); //Determine attenuatio diffuse += diffuseDiff; gl_FragColor.rgb *= vec3(1.0) / ((vec3(1.0) + ((vec3(1.0) - vec3(u_LightColours[i]))*diffuseDiff))); //The expensive part } diffuse += 0.1; //Add ambient light gl_FragColor.rgb *= diffuse; } Am I making any rookie mistakes? Or am I just being unrealistic about what I can do? Thanks in advance
• By yahiko00
Hi,
Not sure to post at the right place, if not, please forgive me...
For a game project I am working on, I would like to implement a 2D starfield as a background.
I do not want to deal with static tiles, since I plan to slowly animate the starfield. So, I am trying to figure out how to generate a random starfield for the entire map.
I feel that using a uniform distribution for the stars will not do the trick. Instead I would like something similar to the screenshot below, taken from the game Star Wars: Empire At War (all credits to Lucasfilm, Disney, and so on...).

Is there someone who could have an idea of a distribution which could result in such a starfield?
Any insight would be appreciated

• 11
• 12
• 21
• 11
• 28