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OpenGL Rendering many trees

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I have set up a system for rendering specifically trees, which are also generated by my engine. They are divided into basically two groups: trunk/branches and leaves. Both have their own index buffer and texture and they share the same vertex, normal etc. buffers. I decided to try instancing to speed up the OpenGL implementation, but I'm not sure if it will be much use, at least on its own. I have not yet implemented a level of detail, but want first to see how fast rendering can be with only quadtree culling and instancing. The tree instances are also sorted by textures and vertex buffers binds.

I have found that for some reason, rendering the trunk and branches is fast, but rendering the leaves is really slow. The leaves consist basically of triangle pairs, rendered with alpha testing (no blending) and with no face culling. In my test scene, I have 3000 trees, which are frustum culled to less than 1/4. The trunk/branches consist of 2166 indices and the leaves consist of 582 indices. When rendering only the trunk/branches, FPS can be around 60, whereas rendering the leaves only yields around 20 FPS. See the images below:

http://www.perilouspenguin.com/glfps/wp-content/uploads/2012/05/full.jpg
http://www.perilouspenguin.com/glfps/wp-content/uploads/2012/05/leaves.jpg
http://www.perilouspenguin.com/glfps/wp-content/uploads/2012/05/trunks.jpg

First I was thinking that it might be a fillrate problem, as the leaves clearly occupy more screen space. But turning the camera away from the leaves does not seem to make any practical difference. Could this have to do with how indexing or vertex data placement works out for the branches and the leaves? For the branches, a single vertex is referenced around 5 times, whereas for the leaves, only 1 or 2 times. Still, there are a lot less vertices in total for the leaves in the test scene.

I understand that LOD could make all the difference in the end, but I have also tried to reduce the number of leaves, and it does not seem to make a big difference. Even a small amount of leaves per tree seems to kill the frame rate pretty good.

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Are you using mip-maps for your leaves texture ?

If not, you may speed up things by doing so, and also potentially reduce your aliasing. Edited by (ok)

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Are you using mip-maps for your leaves texture ?

If not, you may speed up things by doing so, and also potentially reduce your aliasing.


Yes, I'm using mip-maps.

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Are you using frustum culling ?
If yes, I don't understand why your fps still stalls even if the camera is not facing the leaves.

What is the size of your leave texture ?
Did you try to load a really low one (eg. 1*1) to see if the problem comes from here ?

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Ooops sorry, you are doing quadtree culling yet so there might be unnecessary traversal.
My best guess is to debug your quadtree scheme and make sure no unnecessary trees are processed before or after.

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My best guess is to debug your quadtree scheme and make sure no unnecessary trees are processed before or after.


Actually the quadtree frustum culling is so simple, that it only considers a 2D view frustum, which is independent of the camera pitch. I know that this does not work correctly for all cases, but it is fast and works in most cases. The point being now that it does not change the amount of trees processed, if the camera faces the ground. I have also tried low-resolution texture for the leaves with no improvement.

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Ok so it is not the drawing...

I don't know how you have implemented your quadtree but maybe you could test if some trees located outside the desired area get processed ?

For example, you could try to setup a breakpoint if a candidate tree is outside the desired area just to check. You could also double check if your whole loop or part of it does not get processed several time instead of only once. Check if one of your visible trees does not get considered more than once.

It happens to me all the time, fast(your [color=#282828][font=helvetica, arial, verdana, tahoma, sans-serif]

[background=rgb(250, 251, 252)]trunk/branches[/background]

[/font]) does unfortunately not always mean neat.

Good luck.

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The general steps go roughly like this:

First thing to answer is if the slowdown caused by being CPU-bound or GPU-bound? (or, in very rare cases, bad sequential structure causing both CPU and GPU -bound?)
Use tools like AMD CodeAnalyst, Intel vTune, nVidia Parallel NSight, nVidia PerfHUD, Intel GPA, custom intrusive profiling blocks (Game Programming Gems 1), to profile the CPU and GPU workloads.


If you are CPU bound:
- Identify where the additional CPU time is spent. If it is directly in your code, optimize it.

- If the time is spent inside the graphics driver dll, identify how to reduce draw call count by batching. Group vertex buffers together and atlas textures to achieve this.

If you are GPU bound:
- Look at the GPU instruction call trace to identify if you can optimize redundant state sets.
- Identify whether you are vertex shader, pixel shader, texture load, or framebuffer raster op bound. Optimize the appropriate stages or reduce the workload.

I suspect you are somehow CPU bound, since you say that adding rendering workload that is outside the view frustum still causes slowdown.

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As disabling the leaves does not affect quadtree and increases performance a lot, I dont believe that the quadtree is the problem. I could still double check.

I have not tried to sort the leaves by distance, but I did try sorting the tree objects, after the frustum culling. Did not help either, though I'm not sure how efficient my sorting procedure was (used the stl algorithm to sort the vector of indices to visible trees).

I have never used any actual performance measurement tools, though maybe they would prove useful. Probably takes some time to learn how to use them. Are there any versions for Linux?

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Clb is right, you must measure as much as you can, and NO, you don't really need training for that.
You will be glad to simply check out methods with the highest profiles(the ones on top of the list) and possibly concentrate on/optimize them.

You can also more directly evaluate the time spent between statements with very simple functions.

Just google for c++ profiler/profiling tools.

Bench-marking your code is crucial to evaluate yet if you have enough budget for a specific job before writing it.
It also helps a lot to get extra clues about what's possibly wrong.

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I have used gnu profiler before (I use g++), but usually the data seems useless, as it tends to list functions that just dont seem to be related to the problem at hand. I do realize that it takes some skill to be able to dig out the meaningful data.

I'm not sure if this is related, but I have also found that if I have, say, just one mesh that represents e.g. a hedge, consisting of maybe twenty crossing planes with alpha tested semi-transparent texture with opaque and transparent parts alternating at small scale, then a closeup view will make the rendering to crawl. Why would this happen? I mean, I understand that a large alpha blended polygon would have a large impact, but why alpha tested?

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[background=rgb(250, 251, 252)]but usually the data seems useless[/background]


[/quote]
Sometimes it is hard to figure out the cause of your stalls from the profiler only but if a module function comes on top at your app's run-time, at least you know your app is intensively using it. You must also use timing functions directly in your code to locate bottlenecks.

For your second question, it often depend on your transparency approach. If you use raw blending, you need a clever primitive ordering to get the most of it but sometimes screen door is more appropriate (no back to front order needed).

Check those :
http://www.gamedev.net/topic/599103-issues-with-blending-transparency/

http://www.opengl.org/archives/resources/faq/technical/transparency.htm

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I think I made some progress here. I reduced the rendering code temporarily to a simple form, where I was able to see that textures and vertex buffers are only bound once per whole tree system and nothing is clearly done in excess. Still no improvement. Then I realized that I was still drawing the trees to shadowmaps. This explains why looking at the ground did not affect framerate. I then disabled this feature and then the framerate increased when looking away from the trees. I placed three times more trees, and facing the ground still yielded a good framerate. So I guess that one could think that it is fillrate related. I then tried again sorting the trees, checking that sorting is actually happening, but this did not improve the situation. It is strange that even if I went really close to a tree trunk so that it occluded the whole screen area, there was no improvement. I would have guessed that sorting from front to back would have shown improvement in this case at least.

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Do you suppose it would help significantly, if the leaves were rendered to an off screen target, which would be of low res? There was an article about this sort of thing in gpu gems 3 for particle effects. The problem would be downsampling and obtaining the zbuffer. Does arma2 do something like this? I remember that the trees looked a bit blurry.

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You could try a depth-only z prepass without texture reads or color writes. Or you could try occlusion culling which might be very effective for culling away large numbers of distant trees

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I did a quick tryout with z-pretest. I need to enable alpha writing for the leaves for this. I got some strange flickering artifacts, so meybe I need to use some kind of depth offset. Anyway, there was no improvement. Rendering the leaves without any shaders nor texturing did have a huge impact, though. So the shaders must be somewhat demanding, but z pretest wont seem to save it, or then I'm just doing it wrong.

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Only other thing I can think of is impostors, which can look very good if done right - Oblivion (SpeedTree) faded the tree model out for a flat billboard as close as 50m from the camera, and the treescapes always looked great (imo)

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Try to use alpha to coverage, it´s realy fast and could get you a extra fps.


What do you mean by using alpha? I use alpha testing, which I believe is cheap, but it still yields low framerates.

I also just realized that there is the "discard" function in fragment shaders. I think that this improved the situation slightly, but it's not doing wonders.


Only other thing I can think of is impostors, which can look very good if done right - Oblivion (SpeedTree) faded the tree model out for a flat billboard as close as 50m from the camera, and the treescapes always looked great (imo)


Perhaps this is one way, but I bet it is a fair amount of work to make it fast and still look good. Probably need some fancy texture atlasing and what not.
Occlusion query might help to reduce the overdraw, but I'm suspicous as the meshes are quite low-poly and there are many of them.

Ok so, it is established that the low fps is obtained when the trees are in the view frustum and fill most of the screen. Can one deduce from this, that
the program is limited by fillrate or can there be some more complicated caching between vertex and pixel processing, so that the number of polygons
could still matter?

How do games generally cope with the problem, that if you have e.g. a hedge or a bush consisting of a few hundred overlapping alpha tested polygons and the player goes very
close to this bush? This really seems to crush the framerate even without alpha blending. Is the only way to improve the framerate just to do a precise depth sort from front to back?

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What kind of hardware are you working on? Can you confirm the CPU load while your program is running (simply look at Task Manager, it gives a little clue what's going on).

Alpha testing via discard or clip is always slower than shader without it. Only thing you can do about to not use alpha testing (clip / discard) in shaders which don't need it. Alpha blending of course takes even more fill rate.

Cheers!

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What kind of hardware are you working on? Can you confirm the CPU load while your program is running (simply look at Task Manager, it gives a little clue what's going on).

Alpha testing via discard or clip is always slower than shader without it. Only thing you can do about to not use alpha testing (clip / discard) in shaders which don't need it. Alpha blending of course takes even more fill rate.

Cheers!


My hardware is i7 920 CPU and GTX 260, so should not be too bad.

The CPU load is pretty much 100 % for a single core, regardless of how much stuff is being drawn. I don't limit FPS explicitly.

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The CPU load is pretty much 100 % for a single core, regardless of how much stuff is being drawn.


So can we deduce here that your program may be (at least partly) be CPU bound? If your program was GPU bound, the CPU usage wouldn't be 100%. Of course we have to keep in mind that drawing forest quantity of trees takes its toll too.

Are you doing some CPU intensive stuff every frame? How are you sending your geometry to your GPU?

Cheers!

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[quote name='jmakitalo' timestamp='1338322729' post='4944421']
The CPU load is pretty much 100 % for a single core, regardless of how much stuff is being drawn.


So can we deduce here that your program may be (at least partly) be CPU bound? If your program was GPU bound, the CPU usage wouldn't be 100%. Of course we have to keep in mind that drawing forest quantity of trees takes its toll too.

Are you doing some CPU intensive stuff every frame? How are you sending your geometry to your GPU?

Cheers!
[/quote]

I think the CPU load is 100 % because I'm not limiting the framerate in anyway, so the program updates and draws as frequently as possible. Basically
I have a loop which calls update(), draw() and checkInput(). A frame time is evaluated for each cycle and this is used for updating stuff. Maybe the
updating should be fixed to 30 times per second or something. So even if there is not much to draw, CPU usage is 100 %.

For sending the geometry to GPU, I use static VBO with glDrawElements. I think this part is pretty well managed, as the buffers and textures are bound only once
per tree type, so basically once per drawing the whole test scene. The tree branches and leaves use the same vertex position etc. buffers, but they have their own
index buffers.

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Nothing else to do, I tried some sprite-like tree drawing by using my static mesh renderer. I placed around 8000 meshes consisting of two triangles, to get some feeling how well impostor drawing could look like or perform. At first I got again 30 fps in many places, which seemed a bit depressing. The mesh shader is a bit too complicated with normal mapping and so on, but mesh rendering uses the same system as the actual tree rendering, so states and binds are sorted.

Then I decided to change the order of drawing my terrain and the meshes, and this had a significant impact in cases when the trees block most of the terrain. I got steady 60 fps in such cases. So maybe my terrain fragment program is a bit demanding, but it still does not explain the poor performance with the more detailed trees. I tried also rendering first the detailed trees and then terrain, but there was no gain.

Here are some screenshots of the simple two-triangle trees:

tree1
tree2
tree3

To me it seems that only the few front most trees should be rendered with detail and other could be drawn as it seems in the figure. Of course this
can depend on the tree types. Could work well just for the spruces. I'm also a bit worried about the complexity of impostor scheme implementation. Edited by jmakitalo

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      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.
    • 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
    • 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
    • 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
       
    • By dpadam450
      Sampling a floating point texture where the alpha channel holds 4-bytes of packed data into the float. I don't know how to cast the raw memory to treat it as an integer so I can perform bit-shifting operations.

      int rgbValue = int(textureSample.w);//4 bytes of data packed as color
      // algorithm might not be correct and endianness might need switching.
      vec3 extractedData = vec3(  rgbValue & 0xFF000000,  (rgbValue << 8) & 0xFF000000, (rgbValue << 16) & 0xFF000000);
      extractedData /= 255.0f;
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