I'm making an iOS app and I want to be able to render with individual "layers" so that I can do blending between them and use shaders on each individually before blending them all together and rendering to the screen.
I understand that I will be rendering to Textures and then rendering these textures on top of each other in the framebuffer, but I am not understanding clearly what code needs to be written to follow this procedure. In another answer I found what I want to do, but I don't know what code accomplishes this task: How to achieve multi-layered drawing with OpenGL ES on iOS? (For example how do I "Bind texture 1, then draw it"? What does it mean to "Attach texture 1"?)
I've also looked at Apple's documentation regarding this technique but it isn't very clear about the steps or code for the actual rendering part of the process.
How would I go about doing this? (hopefully with code examples of each step because I haven't understood spotty instructions that expect me to just know what is needed for each step)
Here is an example of what I want to do with this. The spheres would be rendered into a "layer" or Texture2D which I would then pass through the shader, then render on top of a already partially rendered scene. I don't know exactly what kind of openGL code could do that.
You're looking at wrong place. To use OpenGL, you need to study OpenGL, not anything else. Apple doesn't provide any OpenGL documentation because it's an open standard, so the specs are freely published. Apple assumes you're already familiar with it.
OpenGL ES 2.0 spec
manual pages
I think you are having trouble because you don't have understanding of GL specific terms. The spec describes them very well and clearly. So, please read the spec. That will save your time A LOT. Or you will keep the trouble.
Also, I like to introduce a site which has very nice conceptual description of OpenGL pipeline.
http://www.songho.ca/opengl/
This site is targeting desktop GL, and some API may be different a little. Please focus on conceptual understanding. For example, here's an illustration from the site.
For more tutorials, google with proper keyword like OpenGL ES 2.0 tutorials (or how-tos). Here's an example link, and would be helpful. There're also many more tutorials. If spec is too boring, it's also good to have some fun with tutors.
Update
I like to say one more. IMO, the OpenGL is all about drawing triangles. Everything is ultimately converted into triangles in 3D space to represent some shape. Anything else all exists only for optimization. And in most cases, GL chooses batch processing for major optimization strategy. Because overhead of each drawing call is not affordable for most games.
It's hard to start OpenGL ES because it's an optimized version of desktop GL, so all convenient or easy drawing features are stripped off. This is same even on recent version of desktop GL.
So there's no such drawOneTriangle function. Instead GL has something like
make a buffer,
put list of many triangles there
select the buffer for next drawing.
draw all triangles in current buffer at once
delete the buffer.
By using buffer, you don't need to dispatch duplicated data to GPU from CPU. And GL uses this approach everywhere. For example, you don't have such drawOneTriangleWithTexture function to use textures. Instead, you have to
make a buffer
put list of many pixels there (bitmap)
select the buffer for next drawing.
draw all triangles with the texture pixel data in current buffers.
delete the buffer.
Everything overly complex stuffs on GL are all exists for optimization. This may look weird at first, but there're usually very good reasons for the design.
Update 2
Now I think you're looking for render to texture feature. (well actually you already mentioned this…)
You can use a rendered image as a texture source. To do this,
you need to bind a frame-buffer with texture object rather then render-buffer object using some functions like glFramebufferTexture.
Once you render to a texture, and switch frame-buffer to final buffer, and bind the texture you drawn and others, and perform the final drawing. You need two frame buffers: one for render-to-texture, and one for final output.
Related
I'm writing a Unity HLSL shader and I want to buffer the previous pixel to use it in the next iteration. I need this to implement TAA anti-aliasing.
I have a simple Raymarching shader. I create a sphere and use Jittering for optimization. But because of this method, noise appears that needs to be removed using the complex Denoiser method, or more SIMPLE TAA anti-aliasing.
Explanation of the reason for this method: I am not satisfied with the usual TAA anti-aliasing in the form of C# code that works with a ready-made render, because there is a "fading noise" effect, which, for example, can be seen on the Cycles render engine in Blender. I need this not to happen, I need the noise to be removed instantly and calculated during the rendering of the PIXEL, not the FRAME.
I really need help, searched the entire internet for the answer
I've been confronted with the extremely bad drawing Performance of Quartz/Core Graphics.
I don't believe its bad in every scenario, but in my occasion, where i need to redraw something like 3000 short lines frequently, it performs super bad.
Since the Modal (of MVC) is fixed I can not change how it spits out the data (if I could, i would have followed the advice, to only draw the changes, so the lines dont have to be redrawn every frame).
So as a conclusion I am considering using opengl for that purpose and I would like to ask u (experienced) guys for an estimation of how well it could work using opengl, before starting to work into that topic, as it seems by far more difficult
than Quartz.
You almost certainly see a speed performance lift from OpenGL over Quartz, however remember that whereas Quartz uses point to point drawing, OpenGL is based on the use of vertices and vertices points (essentially co-ordinates). You may find you need to do some mid-weight parsing work on your existing data source to re-work it into this vertices point system.
Also keep in mind that drawing text on top of an OpenGL ES object is a tricky task - it can be done (ironically) by using Quartz to generate an image, and then using this image as a texture.
I'd definitely recommend using OpenGL Kit as it will make life a bit easier for you as a beginner to OpenGL. Ray Wenderlich has an excellent starting point tutorial here :
http://www.raywenderlich.com/5223/beginning-opengl-es-2-0-with-glkit-part-1
I've been researching this problem I have and I can't seem to understand it well enough to solve it so I thought I might as well throw it out there and the intelligent bunch might have some ideas. :P
Basically I have been working on a iPhone project for a while where I have the luxury to use all the newest frameworks and target 5.1. So I've been using GLKit and the GLKBaseEffect which have been working just fine for me. The reason I started out with GLKBaseEffect rather then writing my own shaders is that I don't know glsl well. However the requirements have become more precise and the base effect just doesn't seem to cut it any longer.
Since I am already doing all my transforms using the base effect I would prefer if I could keep my base effect intact but add glsl-type shaders on top if that makes any sense.
My old approach look something like this (this is in a loop rendering all objects, where an object contain such things as transforms, a mesh and some other less important things for this problem, such as textures, materials and so on)
ObjectBase *obj = [ResourceManager.shared getObjectNamed:name inScene:sceneName];
GLKMatrix4 modelview = effect.transform.modelviewMatrix;
effect.transform.modelviewMatrix = GLKMatrix4Multiply(effect.transform.modelviewMatrix, obj.transform);
[effect prepareToDraw];
[obj render];
effect.transform.modelviewMatrix = modelView;
Here we fetch an object to render and transform (i.e. translate, rotate and scale) the object then we render it, where the rendering itself fetches the mesh for the object, bind the buffers and render it.
So far so good.
What I would like to do however is that during the [obj render]; call I would like the object to also do something like glUseProgram(someProgram); adding more specialized shader code.
I guess one could argue that I am trying to use the base effect for my vertex shaders and want to use "normal" shaders for my fragment shaders. At least that's what I think I want to do.
I have been trying some things.
I tried to create just the fragment shaders and glUseProgramon it, however it said that I need one vertex and one fragment shader when setting up and compiling it. I've also tried to create an empty vertex shader, which didn't turn out very well, I don't know what happens with that, but I am guessing that it overrule the base effect.
I am leaning toward, in the end, accept that it's probably best to throw out the base effects and just write my own shaders all the way. I just feel like it's a lot of work out the window, so I wanted to see how much of it I can save.
I do understand that my understanding of shaders are the part that gives me the most problems, so please be patient with that fact.
I just wanted to give my conclusions for anyone interested in them.
What I've done is actually thrown out the GLBaseEffect all together and implemented my own shader code.
My biggest problem were that I didn't really understand that it's all or nothing so to speak.
Please I might be wrong, so any corrections to where I am wrong will be greatly appreciated, I really don't want to fool anyone reading this.
What I found out during my endeavors is a couple of key-points:
GLKBaseEffect, is meant to mimic the fixed-function pipeline as seen in earlier versions of OpenGLES. Hence it is wrapping the common shader code so you don't really have to care to much about it. You will have basic functionality but it's not really very extendible.
You can still use the neat features of GLKit such as texture loader, the math library and so on if you write your own shader-code. So if you want something more complicated or customizable (bump mapping, toon shading and so on) it is totally worth rewriting the boiler-plate code needed to render properly. What I did at first was that I used the GLKBaseEffect to orient in the scene since it's quite comfortable and easy to use. However when I wanted to do more (tangent-space normal mapping) I kind of got stuck since I couldn't add to the shader program handled by the GLKBaseEffect.
Shaders are really not as scary as I always thought! I just had no idea what it really meant, and I'm surprised that I've read so much about them and still hadn't understood that basically shaders are programs REPLACING the fixed functionality pipeline. Simple as that.
That's enough rant I guess, just wanted to follow up and add what bits and pieces I've collected this far.
Just as you discovered, you can't just use a fragment shader and leave behind the vertex shader. This is because both have different tasks. Vertex shaders deal with the per-vertex aspects: calculating the vertex data, texture (uv's) etc and finally drawing the faces (triangles). Fragment shaders deal with what exactly will be drawn at each pixel on the screen (or in the viewport). When you provide only a fragment shader, you are not telling what your vertex data is, rather you are only telling OpenGL to do something on the pixels. And these pixels hold nothing/gibberish (I am not sure which) since your vertex shader did not do anything.
When using GLKEffect, a call to the [yourEffect prepareToDraw] method takes care of the shaders etc.
If you just wish to use a stock shader pair, why not use the one provided in the XCode OpenGL game template? When you run it, it has two cubes, one rendered using GLKit, and other the normal way. Though I think it will not be enough for most effects. In case you wish to know more about shaders, you can have a look at the NeHe GLSL introduction article. It is about GLSL and how you can write and use shaders in your code. You might want to have a look at Diney Bomfim's All About Shaders articles and this page.
Using GLKit is nice in most cases, since it saves you from writing lots of useless, repetitive code. For example, you do not have to go through so many image formats with different color codings and bits per pixel (per format) and all when you can just use GLKTextureLoader.
Greetings each and all.
I've been struggling with OpenGL ES 2.0 and a particular problem for the last few days now. I'm looking to implement a Geometry Wars clone, for the iPhone, for fun and to learn this technology. So, my background in 3d programming is fairly good, although mainly concentrated around vector mathematics rather then draw calls towards the graphical API, as I've been working with DirectX on and off for the last couple of years. The problem, however, is that I've mainly been working with bigger meshes, loading, translating and transforming them in several ways and now I find myself in a position where I want to handle small meshes, and lots of them.
The objects are triangles, rectangles, hexagons etc. and I want the ability to modify them all separately (eg making the other edge wavy or pulsating). When I've worked with multiple big meshes I've made separate draw calls for them, easily attaching shaders and their respective parameters, but in this case I would like to render it all in one call and there's where my knowledge fails me.
So, to clearify my question. How are you to modify small meshes, preferably stored in one vertex array, individually and render them all at once using shaders with OpenGL ES 2.0?
Although code examples are more then welcome, a "simple" explanation would be enough to get me started. I assume I'm missing something trivial here and any help is greatly appreciated.
Thanks in advance,
Karl
Sounds like Instancing (and instanced arrays) can be an answer to your problem, although it might be a bit too advanced for iOS or ES in general to be supported. This way you can render many copies of the same geometry with per instance data (like a specific texture index or sub-texture or shader parameters). But of course, you cannot render different objects with completely different shaders in one draw call.
Otherwise the much simpler (and maybe much less optimized) function glMultiDrawArrays/Elements renders multiple completely different geometries in one call, but you cannot tell which triangle belongs to which object in the shader and I also doubt that it gives that much of a performance boost.
I'm really new to OpenGL, which is a really bad thing to me :|
I need to draw a star(sort of) with openGl but I'm not really sure where I should start.
The results should be something like this:
Is there an easy way to do this?
the easiest way would be to draw a texture mapped quad with a "star" texture. You can read a tutorial on texture mapping here: http://nehe.gamedev.net/data/lessons/lesson.asp?lesson=06
That tutorial teaches how to draw a cube using textures.
You just have to draw a single face, instead of all six.
The tutorial is written in C++, but near the end you can download the source of a Delphi version.
There are other effects you might want to add later, such as transparency. You can also read about that in the NeHe site. It has a lot of useful tutorials on OpenGL. It's a great place to learn OpenGL.
If you're new to OpenGL and if you're using Delphi, then most probably what you need is GLScene. Mature, alive, very good quality of code and, of course, free.
Why not write an algorithm to generate a texture procedurally in code using a 2D GLuByte array as in the "checker.c" example in Redbook? Instead of following a perfect checkerboard pattern, figure out how to make a 2D texture of that star and map it into a quad using glTexImage2D(...).