I am writing a small game (it is 2d) in IOS using Opengl as a way to get comfortable with opengl. I am using the Texture2D class from the CrashLanding demo. I am using this to generate text for the score. When the text is drawn it is upside down. In the code there is comments about the texture being loaded upside down but I can not find a way to render it the correct way. Any help would be greatly appreciated.
OpenGL and your image loading code do not agree on where the origin is. OpenGL starts in the lower left hand corner, while your picture starts in the upper right hand corner. You can apply a transform to the picture in your app like the CrashLanding demo does. Or even simpler pre flip the image in an editing program such as Photoshop. This will work if your image will only be used as an OpenGL texture in this app. If you need to display this same picture elsewhere you'll need to keep a non flipped version, or figure out how to apply the transform.
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I'm working on an app based on Apple's GLPaint sample code. I've changed the clear color to transparent black and have added an opacity slider, however when I mix colors together with a low opacity setting they don't mix the way I'm expecting. They seem to mix the way light mixes, not the way paint mixes. Here is an example of what I mean:
The "Desired Result" was obtained by using glReadPixels to render each color separately and merge it with the previous rendered image (i.e. using apple's default blending).
However, mixing each frame with the previous is too time consuming to be done on the fly, how can I get OpenGL to blend the colors properly? I've been researching online for quite a while and have yet to find a solution that works for me, please let me know if you need any other info to help!
From the looks of it, with your current setup, there is no easy solution. For what you are trying to do, you need custom shaders. Which is not possible using just GLKit.
Luckily you can mix GLKit and OpenGL ES.
My recommendation would be to:
Stop using GLKit for everything except setting up your rendering
surface with GLKView (which is tedious without GLKit).
Use an OpenGl program with custom shaders to draw to a texture that is backing an FBO.
Use a second program with custom shaders that does post processing (after drawing above texture to a quad which is then rendered to the screen).
A good starting point would be to load up the OpenGl template that comes with Xcode. And start modifying it. Be warned: If you don't understand shaders, the code here will make little sense. It draws 2 cubes, one using GLKit, and one without - using custom shaders.
References to start learning:
Intro to shaders
Rendering to a Texture
Shader Toy - This should help you experiment with your post processing frag shader.
GLEssentials example - This shows how to render to texture using OpenGL ( a bit outdated.)
Finally, if you are really serious about using OpenGL ES to it's full potential, you really should invest the time to read through OpenGL ES 2.0 programming guide. Even though it is 6 years old, it is still relevant and the only book I've found that explains all the concepts correctly.
Your "Current Result" is additive color, which is how OpenGL is supposed to work. To work like mixing paint would be substractive color. You don't have control over this with OpenGL ES 1.1, but you could write a custom fragment shader for OpenGL ES 2.0 that would do substractive color. If you are blending textures images from iOS, you need to know if the image data has been premultiplied by alpha or not, in order to do blending. OpenGL ES expects the non-premultiplied format.
You need to write that code in the function which is called on color change.
and each time you need to set BlendFunc.
CGFloat red , green, blue;
// set red, green ,blue with desire color combination
glBlendFunc(GL_ONE, GL_ONE_MINUS_SRC_ALPHA);
glColor4f(red* kBrushOpacity,
green * kBrushOpacity,
blue* kBrushOpacity,
kBrushOpacity);
To do more things by using BlendFunc use this link
Please specify if it works or not. It work for me.
I am building a 3D image viewer which has Three.JS plane geometries as placeholders with the images as their textures.
Now I want to add a black border around the image. The only way I have found yet to implement this is to add a new black plane geometry behind the image to be displayed. But this required whole-sale changes to my framework which I want to avoid.
WebGL's texture loading function gl.texImage2D has a parameter for border. But I couldn't find this exposed anywhere through Three.js and doubt that it even works the way I think it does.
Is there an easier way to add borders around textures?
You can use a temporary regular 2D canvas to render your image and apply any kind of editing/effects there, like paint borders and such. Then use that canvas image as a texture. Might be a bit of work, but you will gain a lot of flexibility styling your borders and other stuff.
I'm not near my dev machine and won't be for a couple of days, so I can't look up an example of my own. This issue contains some code to get you started: https://github.com/mrdoob/three.js/issues/868
My iOS application draws into a bitmap (same size as my view) using Core Graphics. I want to push updated regions of the bitmap to the screen. (I've used the standard UIView drawRect method but I have some good reasons to switch to OpenGL).
I just want to replicate the same behavior as UIView/CALayer drawRect but in an OpenGL view. Essentially I would like to update dirty rectangles on my OpenGL view. Nothing more.
So far I've been able to create an OpenGL ES 1.1 view and push my entire bitmap on screen using a single quad (texture on a vertex array) for each update of my bitmap. Of course, this is pretty inefficient since I only need to refresh the dirty rectangle, not the whole view.
What would be the most efficient way to do that in OpenGL ES? Should I use a lattice of quads and update the texture of the quads that intersect with my dirty rectangle? (If I were to use that method, should I use VBO?) Is there a better way to do that?
FYI (just in case), I won't need rotation but will need to scale the entire OpenGL view.
UPDATE:
This method indeed works. However, there's a bug in iOS5.x on retina display devices that produces an artifact when using single buffering. The problem has been fixed in iOS6. I don't yet have a work around.
You could simply just update a part of the texture using TexSubImage, and redraw your standard full-screen quad, but with the scissor rect beeing set (glScissor) to the "dirty" part. The GL will then not draw any fragments outside this rect.
For this to work, you must of course use single buffering.
Im working on a painting app which has a tool to brush similar to a painting brush. I've implemented so far through cocos2d, a format like the image
. But my client wants clear edged texture as the image Also the color of the former image is some what blurring indeed. How I can reduce blurring of the sprite image? The image I am using as a texture is the image. Im using a code derived from the Cocos2d RenderTextureTest.
Also, the blend function Im using like in the below code
[brush setBlendFunc:(ccBlendFunc){GL_ONE, GL_ONE}];
[brush.texture setAliasTexParameters];
where, brush is my sprite with the above mentioned texture.
Is there any other way to get the sharp edges as in the later image? Or how I can make the image stop blurring? I am struggling it for last few months. Please some experts look into this and help me.
Im starting with XNA and i need an advice about the following.
I have a .jpg file with my space ship game background with the following size:
width: 5000px
height: 4800px
When i try to load the texture i get the following error:
Texture width or height is larger than the device supports
What is the most used technique to move the background at the same time that your ship is moving?
Thanks a lot.
Kind Regards.
Josema.
One way would be to separate your image into smaller tiles and draw the visible ones.
However this technique suffers from a problem when bilinear sampling is used, because the colors bleeds from the one side of the texture to the other. You can probably compensate by disabling texture WRAP sampling or by grabbing a single of pixels from the tiles next to.
For example if you want 256x256 textures, you would only display 255x255 tiles, because one line (right and bottom) is a copy from the tiles next to it.
Hope it makes sense, otherwise I'll have to paint a picture :-)
The texture limit is determined by graphics card, I believe.
You want to break the texture down to smaller images.
Try something like this. He's tiling a simple 40x40, but you might use it a a guideline on how to tile yours.
http://forums.xna.com/forums/p/19835/103704.aspx
To move the background at the same time that your ship is moving you can implement a camera.
The following links might help-
http://adambruenderman.wordpress.com/2011/04/05/create-a-2d-camera-in-xna-gs-4-0/
http://www.dreamincode.net/forums/topic/237979-2d-camera-in-xna/