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(...).
Related
I have a problem in which in my game I have to use SpriteSortMode.Texture because I have a lot of objects with few textures, so I cannot afford to use SpriteSortMode.BackToFront.
The thing is this means I cannot draw by layers, unless I do SpriteBatch.Begin with the exact same settings, which is what I'm currently doing.
I only have 3 draw layers I need - a Tileset surface, Objects like rocks or characters on the surface, and UI.
Other solutions I've found is using texture quads (which supposedly also improves tileset drawing performance), going 3D with orthogonal view which I haven't researched yet.
I'm hoping there's a better to make this work.
Why would having a lot of objects with few textures mean you have to use SpriteSortMode.Texture?
"This can improve performance when drawing non-overlapping sprites of uniform depth." says the MSDN page, and this is clearly not what you are doing.
Just use the default SpriteSortMode.Deferred and draw things back to front in order.
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.
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 understand that cocos2d it's really simple API, and that I can use it to do simple and huge 2D or even sometimes 3D games/applications. As well I understand that OpenGL it's more complicated, it's lower level API etc.
Question: What is better for implementing 2D/3D games? Why do we need to learn OpenGL if we have simple frameworks like cocos2d? What you can do with OpenGL that you can't do with cocos2d?
Thanks in advance!
What is better for implementing 2D/3D games?
Hard to tell, but a higher level API is always there to make things easier for you. For example you are writing a 2D shootem up. You will likely use a game loop, you will want to use sprites and make those move on the screen. You may want animations like explosions taking place. You'll end up writing your own higher level API to do those things. Cocos2D has solved those problems for you already. Any other frameworld should have solved it.
Why do we need to learn OpenGL if we have simple frameworks like cocos2d?
In case you like to cusomize the standard behaviour of a framework, especially the drawing part, you should get into openGL. If there is something you like to have which doesn't come out of the box you may find yourself reimplementing a base framework class. For example, look at the shaders used in Cocos2D 2.0. If you like some special blending mode, like a tinting effect, you won't get it for free. There is a colour attribute for a CCSprite but this may not be the result you're expecting. So you'll have to write your own shader and plug it into the sprite you like to be displayed in a different way.
What you can do with OpenGL that you can't do with cocos2d?
This comparison doesn't really work out, since cocos2d facilitates opengGL for the drawing part to build up that higher level api and make your life easier as a game developer.
Cocos2d is a wrapper around the 2D features of OpenGL (as of this: http://www.cocos2d-iphone.org/about) . Under the hood it itself uses OpenGL ES to implement its features. This is good because it means that there will be minimal performance overhead so you can start using its simpler API without having to get immersed to the definitely bigger learning path of OpenGL.
It has however only strong 2D support and if you plan to write later 3d games you loose all benefits of Cocos2d: why would you rewrite a 3d rendering engine with a 2d framework that under the hood uses a very strong 3d engine? You loose performance for a lot of unnecessary work.
So the simpler answer is: for 2d Cocos2d, for 3d OpenGL.
If you want to start OpenGL ES, this is a very good tutorial for beginners: http://iphonedevelopment.blogspot.it/2009/05/opengl-es-from-ground-up-table-of.html
I am trying to write a strategy game using XNA 4.0, with a dynamically generating map, and it's really difficult to create all the ground textures, having to distort them individually in photoshop.
So what I want to do is create a flat image, and then apply the distortion programatically to simulate perspective, by moving the corners of the image.
Here is an example done in photoshop:
How can I do that in XNA?
My answer isn't XNA-specific as I've never actually used the library; however the concept should still apply.
In general, the best way to get a good perspective effect is to actually give 3d coordinates and transformations and let DirectX/OpenGL handle the rest. This has great benefits over attempting to do it yourself - specifically, ease of use, performance (much of the work is passed on to your graphics card), and perspective-correct texturing. And nothing's stopping you from doing 3d and 2d in the same scene, if that's a concern. There are numerous tutorials online for getting set up in the third dimension with XNA. I'd suggest heading over to MSDN.