How do I get the maximum number of possibly allocated framebuffers in WebGL? I assume you use getParameter but I don't know what to pass in it. For the maximum amount of color attchements I know I can pass MAX_DRAW_BUFFERS_WEBGL, but i don't know about allocated framebuffers.
Also what does the WebGL 1.0 and 2.0 specs say for the minimum required number of framebuffers possibly allocated and color attachments that can be drawn to and attached at once?
Thanks in advance!
There is no hard limit on framebuffers, after all they're not resource intensive, their attachments are.
As to the number of supported color attachments, according to section 6.8 in the WebGL 1 spec:
The following combinations of framebuffer object attachments, when all of the attachments are framebuffer attachment complete, non-zero, and have the same width and height, must result in the framebuffer being framebuffer complete:
COLOR_ATTACHMENT0 = RGBA/UNSIGNED_BYTE texture
COLOR_ATTACHMENT0 = RGBA/UNSIGNED_BYTE texture + DEPTH_ATTACHMENT = DEPTH_COMPONENT16 renderbuffer
COLOR_ATTACHMENT0 = RGBA/UNSIGNED_BYTE texture + DEPTH_STENCIL_ATTACHMENT = DEPTH_STENCIL renderbuffer
So that's minimum required number of color attachments: 1
There's no required minimum number of enabled draw buffers(=attachments) in the WebGL 2 spec nor in the ES 3.0 spec, instead it's implementation specific and needs to be queried through the means you already mentioned, I believe the defacto minimum to be 4 though.
Related
I am working on my Multiple Render Target pipeline and I came across a curiosity in the docs that I don't fully understand and googling for an hour hasn't helped me find a clear answer.
You utilize gl.drawBuffers([...]) to link the locations used in your shader to actual color attachments in your framebuffer. So, most of the expected parameters makes sense:
gl.NONE - Make the shader output for this location NOT output to any Color attachment in the FBO
gl.COLOR_ATTACHMENT[0 - 15] - Make the shader location output to the specified color attachment.
But then we have this mysterious target (from the docs):
gl.BACK: Fragment shader output is written into the back color buffer.
I don't think I understand what the back color buffer is, especially relative to the currently attached FBO. As far as I know you don't specify a 'back color buffer' when making a FBO...so what does this mean? What is this 'back color buffer'?
In WebGL the backbuffer is effectively "the canvas". It's called the backbuffer because sometimes there is a frontbuffer. Canvas's in WebGL are double buffered. One buffer is whatever is visible, the other is the buffer you're currently drawing to.
You can't use [gl.BACK, gl_COLOR_ATTACHMENT0]
When writing to a framebuffer each entry can only be the same attachment or NONE. For example imagine you have 4 attachments. Then the array you pass to drawBuffers is as follows
gl.drawBuffers([
gl.COLOR_ATTACHMENT0, // OR gl.NONE,
gl.COLOR_ATTACHMENT1, // OR gl.NONE,
gl.COLOR_ATTACHMENT2, // OR gl.NONE,
gl.COLOR_ATTACHMENT3, // OR gl.NONE,
])
You can not swap around attachments.
gl.drawBuffers([
gl.NONE,
gl.COLOR_ATTACHMENT0, // !! ERROR! This has to be COLOR_ATTACHMENT1 or NONE
])
You can't use gl.BACK gl.BACK is only for when writing to the canvas, in other words then the frame buffer is set to null as in gl.bindFramebuffer(null);
gl.drawBuffers([
gl.BACK, // OR gl.NONE
]);
note: drawBuffers state is part of the state of each framebuffer (and canvas). See this and this
I'm developing a opengl es application for ios.
I'm trying to blend two textures in my shader, but I always get only one active texture unit.
I have generated two texture, and linked them with two "sampler2D" from the fragment shader.
I set them to unit 0 and 1 by using glUniform1f();
And I have bind the textures using a loop
for (int i = 0; i < 2; i++)
{
glActiveTexture(GL_TEXTURE0 + i);
glBindTexture(GL_TEXTURE_2D, textures[i]);
}
But when I draw the opengl frame, only one unit is active. like in the picture below
So, what I've been doing wrong?
The way I read the output of that tool (I have not used it), the left pane shows the currently active texture unit. There is always exactly one active texture unit, corresponding to your last call of glActiveTexture(). This means that after you call:
glActiveTexture(GL_TEXTURE0 + i);
the value in the left circled field will be the value of i.
The right pane shows the textures bound to each texture unit. Since you bound textures to unit 0 and 1 with the loop shown in your question, it shows a texture (with id 201) bound to texture unit 0, and a texture (with id 202) bound to texture unit 1.
So as far as I can tell, the state shown in the screenshot represents exactly what you set based on your description and code fragment.
Based on the wording in your question, you might be under the impression that glActiveTexture() enables texture units. That is not the case. glActiveTexture() only specifies which texture unit subsequent glBindTexture() calls operate on.
Which textures are used is then determined by the values you set for the sampler uniforms of your shader program, and by the textures you bound to the corresponding texture units. The value of the currently active texture unit has no influence on the draw call, only on texture binding.
I have a texture which I use as a texture map. Its a 2048 by 2048 texture divided in squares of 256 pixels each. So I have 64 "slots". This map can be empty, partly filled or full. On screen I am drawing simple squares with a slot of the sprite map each.
The problem is that I have to update this map from time to time when the asset for the slot becomes available. These assets are being downloaded from the internet but the initial information arrives in advance so I can tell how many slots I will use and see the local storage to check which ones are already available to be drawn at the start.
For example. My info says there will be 10 squares, from these 5 are available locally so when the sprite map is initialized these squares are already filled and ready to be drawn. On the screen I will show 10 squares. 5 of them will have the image stored in the texture map for those slots, the remaining 5 are drawn with a temporal image. As a new asset for a slot is downloaded I want to update my sprite map (which is bound and used for drawing) with the new corresponding texture, after the draw is finished and the sprite map has been updated I set up a flag which tells OpenGL that it should start drawing with that slot instead of the temporal image.
From what I have read, there are 3 ways to update a sprite map.
1) Upload a new one with glTextImage2D: I am currently using this approach. I will create another updater texture and then simply swap it. But i frequently run into memory warnings.
2) Modify the texture with glTextSubImage2D: I cant get this to work, I keep getting memory access errors or black textures. I believe its either because the thread is not the same or I am accessing a texture in use.
3) Use Frame Buffer Objects: I could try this but I am not certain if i can Draw on my texturebuffer while it is already being used.
What is the correct way of solving this?
This is meant to be used on an iPhone so resources are limited.
Edit: I found this post which talks about something related here.
Unfortunately I dont think its focused on modifying a texture that is currently being used.
the thread is not the same
OpenGL-ES API is absolutely not multi-threaded. Update your texture from main thread.
Because your texture must be uploaded on gpu, glTextSubImage2D is the fastest and simplest path. Keep this direction :)
Render on a Frame Buffer (attached on your texture) is very fast for rendering data which are already on gpu. (not your case). And yes you can draw on a frame buffer bound to a texture (= a frame buffer which use the texture as color attachment).
Just one contrain: You can't read and write the same texture in one draw call (The texture attached to the current frame buffer can't be bound to a texture unit)
I'm working on an iPad app, with OpenFrameworks and OpenGL ES 1.1. I need to display a video with alpha channel. To simulate it i have a RGB video (without any alpha channel) and another video containing only alpha channel (on every RGB channel, so the white parts correspond to the visible parts and the black to the invisible). Every video is an OpenGL texture.
In OpenGL ES 1.1 there is no shader, so i found this solution (here : OpenGL - mask with multiple textures) :
glEnable(GL_BLEND);
// Use a simple blendfunc for drawing the background
glBlendFunc(GL_ONE, GL_ZERO);
// Draw entire background without masking
drawQuad(backgroundTexture);
// Next, we want a blendfunc that doesn't change the color of any pixels,
// but rather replaces the framebuffer alpha values with values based
// on the whiteness of the mask. In other words, if a pixel is white in the mask,
// then the corresponding framebuffer pixel's alpha will be set to 1.
glBlendFuncSeparate(GL_ZERO, GL_ONE, GL_SRC_COLOR, GL_ZERO);
// Now "draw" the mask (again, this doesn't produce a visible result, it just
// changes the alpha values in the framebuffer)
drawQuad(maskTexture);
// Finally, we want a blendfunc that makes the foreground visible only in
// areas with high alpha.
glBlendFunc(GL_DST_ALPHA, GL_ONE_MINUS_DST_ALPHA);
drawQuad(foregroundTexture);
It's exactly what i want to do but glBlendFuncSeparate() doesn't exist in OpenGL ES 1.1 (or on iOS). I'm trying to do it with glColorMask and i found this : Can't get masking to work correctly with OpenGL
But it doesn't work as well, i guess because his mask texture file contains an 'real' alpha channel, and not mine.
I highly suggest you compute a single RGBA texture instead.
This will be both easier, and faster ( because you're sending 2 RGBA textures each frame - yes, your RGB texture is in fact encoded in RGBA by the hardware, and the A is ignored )
glColorMask won't help you, because it simply says "turn on or off this channel completely".
glBlendFuncSeparate could help you if you had it, but again, it's not a good solution : you're ruining your (very limited) iphone bandwidth by sending twice as much data as needed.
UPDATE :
Since you're using OpenFrameworks, and according to its source code ( https://github.com/openframeworks/openFrameworks/blob/master/libs/openFrameworks/gl/ofTexture.cpp and https://github.com/openframeworks/openFrameworks/blob/master/libs/openFrameworks/video/ofVideoPlayer.cpp ) :
Use ofVideoPlayer::setUseTexture(false) so that ofVideoPlayer::update won't upload the data to video memory;
Get the video data with ofVideoPlayer::getPixels
Interleave the result in the RGBA texture (you can use an GL_RGBA ofTexture and ofTexture::loadData)
Draw using ofTexture::Draw ( this is what ofVideoPlayer does anyway )
so I've discovered that my graphics card automatically resizes textures to powers of 2, which isn't usually a problem but I need to render only a portion of my texture and in doing so, must have the dimensions it has been resized to...
ex:
I load a picture that is 370x300 pixels into my texture and try to draw it with a specific source rectangle
RECT test;
test.left = 0;
test.top = 0;
test.right = 370;
test.bottom = 300;
lpSpriteHandler->Draw(
lpTexture,
&test, // srcRect
NULL, // center
NULL, // position
D3DCOLOR_XRGB(255,255,255)
);
but since the texture has been automatically resized (in this case) to 512x512, I see only a portion of my original texture.
The question is,
is there a function or something I can call to find the dimensions of my texture?
(I've tried googling this but always get some weird crap about Objects and HSL or something)
You may get file information by using this call:
D3DXIMAGE_INFO info;
D3DXGetImageInfoFromFile(file_name, &info);
Though, knowing the original texture size you'll still get it resized on load. This will obviously affect texture quality. Texture resizing is not a big deal when you apply it on mesh (it will get resized anyway) but for drawing sprites this could be a concern. To workaround this I could suggest creating a surface, loading it via D3DXLoadSurfaceFromFile and then copying it to a "pow2" sized texture.
And an offtopic: are you definitely sure about your card capabilities? May be in fact your card do support arbitrary texture sizes but you use D3DXCreateTextureFromFile() which by deafult enforces pow2 sizes. To avoid this try using extended version of this routine:
D3DTexture* texture;
D3DXCreateTextureFromFileEx(
device, file_name, D3DX_DEFAULT_NONPOW2, D3DX_DEFAULT_NONPOW2, D3DX_DEFAULT, 0,
D3DFMT_UNKNOWN, D3DPOOL_MANAGED, D3DX_DEFAULT, D3DX_DEFAULT, 0, NULL, NULL,
&texture);
If your hardware suppors non-pow2 textures you'll get your file loaded as it is. If hardware is not able to handle it than method will fail.