• Announcements

    • khawk

      Download the Game Design and Indie Game Marketing Freebook   07/19/17

      GameDev.net and CRC Press have teamed up to bring a free ebook of content curated from top titles published by CRC Press. The freebook, Practices of Game Design & Indie Game Marketing, includes chapters from The Art of Game Design: A Book of Lenses, A Practical Guide to Indie Game Marketing, and An Architectural Approach to Level Design. The GameDev.net FreeBook is relevant to game designers, developers, and those interested in learning more about the challenges in game development. We know game development can be a tough discipline and business, so we picked several chapters from CRC Press titles that we thought would be of interest to you, the GameDev.net audience, in your journey to design, develop, and market your next game. The free ebook is available through CRC Press by clicking here. The Curated Books The Art of Game Design: A Book of Lenses, Second Edition, by Jesse Schell Presents 100+ sets of questions, or different lenses, for viewing a game’s design, encompassing diverse fields such as psychology, architecture, music, film, software engineering, theme park design, mathematics, anthropology, and more. Written by one of the world's top game designers, this book describes the deepest and most fundamental principles of game design, demonstrating how tactics used in board, card, and athletic games also work in video games. It provides practical instruction on creating world-class games that will be played again and again. View it here. A Practical Guide to Indie Game Marketing, by Joel Dreskin Marketing is an essential but too frequently overlooked or minimized component of the release plan for indie games. A Practical Guide to Indie Game Marketing provides you with the tools needed to build visibility and sell your indie games. With special focus on those developers with small budgets and limited staff and resources, this book is packed with tangible recommendations and techniques that you can put to use immediately. As a seasoned professional of the indie game arena, author Joel Dreskin gives you insight into practical, real-world experiences of marketing numerous successful games and also provides stories of the failures. View it here. An Architectural Approach to Level Design This is one of the first books to integrate architectural and spatial design theory with the field of level design. The book presents architectural techniques and theories for level designers to use in their own work. It connects architecture and level design in different ways that address the practical elements of how designers construct space and the experiential elements of how and why humans interact with this space. Throughout the text, readers learn skills for spatial layout, evoking emotion through gamespaces, and creating better levels through architectural theory. View it here. Learn more and download the ebook by clicking here. Did you know? GameDev.net and CRC Press also recently teamed up to bring GDNet+ Members up to a 20% discount on all CRC Press books. Learn more about this and other benefits here.
Sign in to follow this  
Followers 0
Cornstalks

OpenGL
Drawing lots of 2D boxes; should I batch the draw call, and what's the best way to do that?

12 posts in this topic

When batching draw calls, how does one handle different transform matrices (position/rotation) for each object? Does each object's transformation matrix have to be applied before the batch draw call?

Specifically, I'm using OpenGL ES 2.0 to draw lots of 2D boxes. I can draw each one individually just fine, but seeing as I'm targeting mobile platforms, I'm looking to try to squeeze as much performance out of this as I can. The boxes aren't textured; mostly I'm interested in minimizing draw calls to save CPU time. The more CPU time I save, the larger my physics simulation can be.

[list]
[*]If I draw a lot of boxes and want to batch the draw calls together into one call, does that require that I apply the transformation matrices of each object to its vertices before copying all the objects into a single buffer for drawing?
[*]When batches are drawn, how does one differentiate between each object being drawn (if it's possible)? Perhaps my understanding of batching is wrong, but the way I currently understand it is that you cannot differentiate between each object (because you just take the vertices of all the objects to draw and copy them all into one buffer, so it just looks like a whole bunch of vertices; also this would require using GL_TRIANGLES instead of GL_TRIANGLE_STRIP (unless degenerate triangles were inserted) so as to not connect two different objects with a stray triangle)
[*]If you had a bunch of 2D boxes to draw, each with its own position, rotation, and scaling, but all of the same color (and no textures), how would [i]you[/i] (personally) draw them? As a follow up, what if each had its own color; does that change things?
[/list]

I don't know a lot about drawing optimization techniques. I'm comfortable drawing things to the screen, but I'm not a fancy graphics programmer.
0

Share this post


Link to post
Share on other sites
your understanding is correct
you can:
1. position vertices so that you only need 1 (or 2) matrices to determine their position in space
basically, if you have no choice but to transform them each frame, you can use the animation approach:
use a dynamic VBO, and transform each vertex each frame, and render everything in one go
this is a reasonable approach in many cases

2. use several draw calls: use one matrix that you translate back and forth, draw a range of vertices at a time
glDrawArrays takes 3 parameters: type, first, and count
so you would use the first parameter, and start with 0, then jump to say 4, 8, 12, 16.. if you only draw 1 box at a time
this is very slow though, so if you can, draw 100 boxes at a time :)

i use both, since if you have alot of vertices it may not be in your best interest to transform all of them each frame
instead using a few extra calls on groups of vertices that belong together is better
but it depends on your data
i'm sure other people can name other solutions, but as long as your boxes don't move, you should be able to do one or the other without problem
Edited by Kaptein
1

Share this post


Link to post
Share on other sites
[quote name='Kaptein' timestamp='1352298660' post='4998416']
your understanding is correct
you can:
1. position vertices so that you only need 1 (or 2) matrices to determine their position in space
basically, if you have no choice but to transform them each frame, you can use the animation approach:
use a dynamic VBO, and transform each vertex each frame, and render everything in one go
this is a reasonable approach in many cases
[/quote]
That's one option I'm considering.

[quote name='Kaptein' timestamp='1352298660' post='4998416']
2. use several draw calls: use one matrix that you translate back and forth, draw a range of vertices at a time
glDrawArrays takes 3 parameters: type, first, and count
so you would use the first parameter, and start with 0, then jump to say 4, 8, 12, 16.. if you only draw 1 box at a time
this is very slow though, so if you can, draw 100 boxes at a time :)
[/quote]
Well, each box has its own transformation matrix because they're all independently movable, so I'm guessing this would require drawing one box at a time (using this method)?

[quote name='Kaptein' timestamp='1352298660' post='4998416']
i'm sure other people can name other solutions, but as long as your boxes don't move, you should be able to do one or the other without problem
[/quote]
The boxes certainly move, as they're part of a physics simulation, which unfortunately is what makes this complicated.

[quote name='BitMaster' timestamp='1352301153' post='4998427']
I don't have a lot of experience on mobile platforms, but shouldn't the glDraw*Instanced family of calls solve your problem?
[/quote]
I can certainly draw with them, but I'm trying to find ways to a) minimize the number of draw calls and b) put as much of the computation on the GPU instead of the CPU. I don't know how to draw things in batches without first applying each object's transformation matrix to all of its vertices on the CPU, and then using the transformed data in the draw call. I don't know if there's a different/better way to do this, because right now the options I'm seeing are a) make a draw call for each object and don't apply the transformations on the CPU, or b) apply the transformations on the CPU and make a batched draw call. I'm debating between the two and am interested if a third option exists.

[quote name='BitMaster' timestamp='1352301153' post='4998427']
You have one VBO containing the box geometry. In your shader you then have something like this
[code]
#define MAX_INSTANCE SomeReasonableValue

uniform mat4 mvp[MAX_INSTANCES];
...
outVertex = mvp[gl_InstanceID] * inVertex;
[/code]
[/quote]
That's a neat idea, but glDraw*Instanced() drawing didn't appear until OpenGL ES 3.0, and I'm stuck with 2.0 :(
0

Share this post


Link to post
Share on other sites
For GLES 2.0 you have no choice but to do the transformation on CPU and load a dynamic VBO each frame if you have dynamic objects you want to batch.

On the plus-side, you have less calculations in your shader and can use that extra performance for making the pixels prettier. (or draw more boxes before GPU-limit) Edited by Olof Hedman
0

Share this post


Link to post
Share on other sites
What about adding N box geometries to the same VBO, just one after the other. For each geometry, add an additional integer attribute which is constant for each box (0 to N-1). Then you have basically a handrolled glDraw*Instanced in batches of maximal N, with your integer attribute taking the role of gl_InstanceID. Edited by BitMaster
0

Share this post


Link to post
Share on other sites
[quote name='BitMaster' timestamp='1352304076' post='4998448']
What about adding N box geometries to the same VBO, just one after the other. For each geometry, add an additional integer attribute which is constant for each box (0 to N-1). Then you have basically a handrolled glDraw*Instanced in batches of maximal N, with your integer attribute taking the role of gl_InstanceID.
[/quote]

You'd need to do add that attribute for each vertex, so a lot of extra integers.
I guess you'd have to put the matrixes in a texture too.
My gut says it will be slower then just transform on CPU, but I can't say I know Edited by Olof Hedman
0

Share this post


Link to post
Share on other sites
Hmm, I think I disregarded the case of 2D and only trivial shading.

If so, I guess more unorthodox methods could yield result, specially if the rest of the simulation tax the CPU.

The vertexes on a 2D box is less data then a matrix though, so I still say an efficient CPU-transform is probably the best :)
0

Share this post


Link to post
Share on other sites
Well, that will largely depend on exactly which transformations are needed. In the pure 2D case you can get away with a mat2x3 and still be completely general. For translation with rotation you can get away with a single vec3 (2D translation and angle) or maybe a vec4 (2D translation and precalculated sin(angle) and cos(angle)). I guess the 'best' solution to this problem will be extremely domain-specific, so the more ideas Cornstalks has lying around, the better. Edited by BitMaster
0

Share this post


Link to post
Share on other sites
The one recommendation I haven't seen is to consider jumping up to ES3. Now, that may not be viable for you, but if it is you'll have instancing support, so happy days - you're in the promised land.

If you can't do that then you've got a balancing act between the cost of splitting batches versus the cost of updating your vertex data in a manner that would allow you to take it all in a single batch.

For a desktop implementation without either instancing or glMapBufferRange (which would be required to update VBOs in a reasonable manner and without stalling the pipeline - again, ES3 would make that problem go away too) my gut inclination would be to drop the use of VBOs altogether, use client-side arrays in system memory, and transform on the CPU. Note that I said "[i]desktop[/i]" here; I'm not certain how much of the following is going to apply to a mobile implementation so take it with the appropriate sized grain of salt.

Before proceeding it needs to be noted that ES2 [i]does[/i] allow use of client-side arrays in this manner.

The main rationale behind this is that updating a VBO can be a horribly expensive operation - if you get it wrong it can be orders of magnitude more expensive than just not using VBOs at all. The reason why is that if the VBO is currently in use for drawing your program will not be able to immediately update it - instead it must stall, wait for all pending drawing operations to complete, then the update can happen. Do this a few too many times per frame and some implementations will plunge you to single digit framerates.

I'm guessing that you don't really want that to happen. ;)

So lets look at transforming a box on the CPU. This is not as horrible as it may appear at first glance.

First thing is to use indexed drawing (via glDrawElements) which will reduce the amount of vertices that need to be transformed from 24 to 8 - that's quite a significant saving already.

Second thing is to look at the transformation itself. There are several shortcuts you can take here, with an obvious one being to check if the box needs to be rotated - if it doesn't then the transformation collapses from a full set of matrix calculation/multiplies to 3 additions. Nice! The same applies to scaling; again you can collapse the full transform to something much much simpler (and faster).

One other factor here is that the indices used for drawing many boxes are going to be static - they'll never change, so you can just set them up once and reuse them as needed. You'll need to burn a bit of extra memory to set up indices for multiple boxes, but I believe that the tradeoff is worth it.

You could also get a further reduction in vertex submission by just not bothering to draw cube faces that are facing away from the viewpoint, but that would mess things up a little with your static indices (although you could work around it by collapsing them to 0-area triangles and reusing the same vertex for all of them). I'd maybe save that one for a later avenue of potential optimization if needed.

If my advice about VBOs turns out to be wrong on mobile platforms (i.e. if the cost of updating is lower than I estimate) then you're in a nice position where you can use a dynamic VBO, a static index buffer, and just fill/draw. I'm not sure if I'd be happy mixing client-side vertex data with an index buffer though, but my limited experience of mobile platforms measn that I can't really comment further on that one.
1

Share this post


Link to post
Share on other sites
Yeah, the best option will likely be very specific to my case. Specifically, this is a 2D game on Android where I'm using Box2D to simulate physical interactions of a large number of 2D boxes/rectangles. The boxes are not textured, and at the moment I'm considering making them all one color. The boxes can freely move and rotate during the simulation. Box2D gives me a translation vector (x and y) and rotation vector (precomputed sin and cos) for each box, and I know each box's size (I'm considering making them all the same size).

[quote name='mhagain' timestamp='1352307780' post='4998470']
The one recommendation I haven't seen is to consider jumping up to ES3. Now, that may not be viable for you, but if it is you'll have instancing support, so happy days - you're in the promised land.
[/quote]
Unfortunately, I can't, as I'm targeting Android devices and the best thing available is ES2.0.

[quote name='mhagain' timestamp='1352307780' post='4998470']
First thing is to use indexed drawing (via glDrawElements) which will reduce the amount of vertices that need to be transformed from 24 to 8 - that's quite a significant saving already.
[/quote]
These are 2D boxes, so the savings are significantly reduced (but still present). Are the savings still significant enough, do you think?

One thought I've had (there's a problem with it though) is to make one buffer that holds transformation matrices (really just vec4s representing the object's translation and rotation vectors) for every object, and then when drawing use an index array to index into the transformation matrix buffer. That way, each vertex can reference the corresponding box's transformation matrix and the box's transformation matrix only needs to be sent once. Each update would require updating the transformation matrix buffer. The problem, however, is another vertex buffer would be needed to define the 4 vertices for each box. This other vertex buffer only needs 4 elements, as all the boxes can be represented with the same vertices and a different transformation matrix. However, I don't think I can specify two index buffers, one which indexes into the transformation matrix buffer and the other which indexes into the little vertex buffer.

I'm seriously considering abandoning batching altogether at this point and just drawing each box individually (and transforming on the GPU using a uniform matrix passed in). Vertex data and buffer indices remain the same for each draw call. The only thing that would change is the uniform matrix. Thoughts?
0

Share this post


Link to post
Share on other sites
Hmmm - when I saw the word "box" I automatically assumed a 3D shape (even if projected onto a 2D view), but could you clarify - are you talking "boxes" as I assumed with 6 sides, 8 corners, or are you talking rectangles? I'd withdraw a huge chunk of my previous post if the latter (and happily accept negative rep on it too).

[quote name='Cornstalks' timestamp='1352313224' post='4998519']
I'm seriously considering abandoning batching altogether at this point and just drawing each box individually (and transforming on the GPU using a uniform matrix passed in). Vertex data and buffer indices remain the same for each draw call. The only thing that would change is the uniform matrix. Thoughts?
[/quote]

Worth benchmarking and seeing how you go. It's incredibly simple to implement and may turn out to be not a problem at all. Edited by mhagain
0

Share this post


Link to post
Share on other sites
[quote name='mhagain' timestamp='1352335222' post='4998663']
Hmmm - when I saw the word "box" I automatically assumed a 3D shape (even if projected onto a 2D view), but could you clarify - are you talking "boxes" as I assumed with 6 sides, 8 corners, or are you talking rectangles? I'd withdraw a huge chunk of my previous post if the latter (and happily accept negative rep on it too).
[/quote]
Boxes as in 2D rectangles and squares. 4 vertices, 2 triangles. I voted you up because even though a good amount of what you were talking about doesn't really apply in my particular case, there are things that you mentioned that I do appreciate because they may be very helpful in future projects.

I've got some basic rendering working now using the method in my last paragraph of my previous post. I plan on doing some stress testing and benchmarking and seeing if the rendering is enough of a bottleneck to try to optimize more, though I'm doubting it will at this point.
0

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!


Register a new account

Sign in

Already have an account? Sign in here.


Sign In Now
Sign in to follow this  
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!
    • By Solid_Spy
      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.
       
      Vertex Shader
      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
  • Popular Now