trying to figure out how I can render a shadow on an invisible plane, so the background of my sceneView shows through.
THREE.js has a ShadowMaterial which does exactly this - only the shadow is rendered.
Current thinking is to make a custom Metal shader which looks straightforward, but i'm unsure how to go about knocking out the floor to show everything aside from the shadow.
Here's an example of a shadow catcher: https://knowledge.autodesk.com/search-result/caas/sfdcarticles/sfdcarticles/Maya-2015-Shadow-Catching-with-Use-Background-material.html
Ok, so check out this example project on Github:
https://github.com/carolight/Metal-Shadow-Map/blob/master/Shadows/Shader.metal#L67
That link is to the shader that performs the shadow map testing. Basically, it normalizes the Z position of the fragment being rendered and compares it to the Z-Buffer of the shadow map. If it is less than the shadow-Z, the pixel is fully lit (line 67) else it is tinted slightly (line 69).
What you want to do instead is write (0,0,0, shadow_opacity) for line 69 and (0,0,0,0) for line 67. This should emit transparent pixels. Set shadow_opacity as a uniform from [0.0..1.0].
The rest of the setup is shown in the example. Tilt the plane/camera to the desired setting, skip drawing the cube/vase/whatever in the main pass if you don't really want it in the scene (line 279). (However, note the shadow pass and keep it there).
Related
I am using OpenGL ES 1.1 to draw lines in my iPad app. I want to make sure that the drawn lines are always visible on the screen regardless of the background colors, and without allowing the user to choose a color. Is there a blend function that will create this effect? So the color of the line drawn will change based on the colors already drawn beneath it and therefore always be visible.
Sadly the final blending of fragments into the framebuffer is still fixed function. Furthermore glLogicOp isn't implemented in ES so you can't do something cheap like XOR drawing.
I think the net effect is that:
you want the output colour to be a custom function of the colour already in the frame buffer;
but the frame buffer can't be read in a shader (it'd break the pipeline and lead towards concurrency issues).
You're therefore going to have to implement a ping pong pipeline.
You have two off-screen buffers. One represents what you output last frame, the other represents what you output the frame before that.
To generate a new frame you render using the one that represents the frame before as an input. Because it's an input you can sample it wherever you want and make whatever calculations you like on it. You render to the other buffer that you have (ie, the even older one) because you no longer care about its contents.
Then you copy all that to the screen and swap the two over, meaning that what you just drew is still in a texture to refer to as what you drew last frame. What you just referred to becomes your next drawing target because it's something you conveniently already have lying around.
So you'll be immediately interested in rendering to a texture. You'll also need to decide what function you want to use to pick a suitable 'different' colour to the existing background. Maybe just inverting it will do?
I think this could work:
glBlendFunc(GL_ONE_MINUS_DST_COLOR, GL_ZERO);
Draw your lines with a white color, and then the result will be rendered as
[1,1,1,1] * ( 1 - [DstR, DstG, DstB, DstA]) + ([DstR, DstG, DstB, DstA] * 0)
This should render a black pixel where the background is white, a white pixel where the background is black, a yellow pixel where the background is blue, etc.
I've created a canvas within which I display an image that is clipped when it goes over the edges. I can do this fine with a square shaped frame, however the frame I want to use is the one below. Is there any way I can clip the image inside the frame without having to add a non transparent square border around the image, i.e. just using the black line that I've already drawn? (on iPad)
You'll need to use Core Graphics and Quartz to handle this sort of clipping/graphics manipulation.
http://developer.apple.com/library/ios/#documentation/GraphicsImaging/Conceptual/drawingwithquartz2d/Introduction/Introduction.html#//apple_ref/doc/uid/TP30001066
If you're using UIBezierPath, you may be able to achieve the clipping you're after using the following process
http://developer.apple.com/library/ios/#documentation/GraphicsImaging/Conceptual/drawingwithquartz2d/dq_paths/dq_paths.html#//apple_ref/doc/uid/TP30001066-CH211-TPXREF101
Convert your UIBezierPath to a CGPath
Get your image into a CGContext
Add your CGPath to the context via CGContextAddPath
Clip your context using CGContextClip
Alternatively, if you don't want to be messing with paths (and depending on whether this technique is suitable for your situation, your description of the issue makes it hard to tell), it might be worth using image masking to achieve the effect you're after. See the first link and look under "Bitmap Images and Image Masks".
I have been looking for the solution on the web for a long time. Most tutorials are fairly simple about adding shadow to a UIView. I also noticed that if we add a shadow to an UIImageView. The shadow shape could perfectly fit the shape of the content image if the image itself has alpha channel in it. Say for example, if the image is an animal with transparent background, the shadow shape is also the same as that animal (not a rectangle shadow as same as UIImageView frame).
But these are not enough. What I need to do is to add some changes to the shadow so it may have some rotation angle and compressed (squeezed or shift) effect so that looks like the sunlight comes from a certain spot.
To demonstrate what I need, I upload 2 images below, which I captured from the Google Map App created by Apple. You can imagine the Annotation Pin is an image which has the Pin shape, so the shadow is also "pin shaped", but it is not simply "offset" with a CGSize, you can see the top of the shadow is shifted right about 35 degrees and slightly squeezed the height.
When we tap and hold and pin, the shadow is also animated away from the pin, so I believe that such shadow can be made programmably.
The best shadow tutorial I can found so far is http://nachbaur.com/blog/fun-shadow-effects-using-custom-calayer-shadowpaths But unfortunately, that cannot make this effect.
If anyone know the answer or know any better words to search for, please let me know. Thank you.
(Please note that the shape of the image is dynamic in the App, so using any tool like Photoshop to pre-render the shadow is not an option.)
In order to create dynamic effects like this, you have to use Core Graphics. It's incredibly powerful once you know how to use it. Basically you need to set a skew transform on the context, set up a shadow and draw the image. You will probably have to use transparency layers as well.
It doesn't sound like you can use CALayer shadows, since that is meant to solve a specific use-case. The approach Apple takes with the pin marks on the map is to have two separate images that are created ahead of time (e.g. in Photoshop) and they position them within the map relative to a reference point.
If you really do need to do this at run-time, it should still be possible by using either Core Graphics or ImageKit. To get a blurred shadow appearance, you can use the kCICategoryBlur CIFilter. You can then convert the image to grayscale. And to get that compressed look you just need to resize and skew the image.
Once you have two separate images, you can either take the CGImageRef for the shadow image and can set that as the content of another sublayer, or you can add it as a separate view.
If you know what all the shapes are, you could just render a shadow image in Photoshop or something.
I'm trying to write a fairly simple animation using Core Animation to simulate a book cover being opened. The book cover is an image, and I'm applying the animations to its layer object.
As well as animating a rotation around the y axis (The the anchorPoint property set of the left of the screen), I need to scale the right hand edge of the image up so it appears to "get closer" to the user and create the illusion of depth. Flipboard, for example, does this scaling really well.
I can't find any way of scaling an image like this, so only one edge is scaled and the image ends up nonrectangular.
All help appreciated with this one!
CoreAnimation, by default, "flattens" its 3D hierarchy into a 2D world at z=0. This causes perspective and the like to not work properly. You need to host your layer in a CATransformLayer, which will render its sublayers as a true 3D layer hierarchy.
Hello I am having a hard time making this UI element look the way I want (see screenshot). Notice the image on the right--how the line width and darkness looks inconsistent compared to the image on the left (which happens to be a screen grab from safari) where the border width is more consistent. How does apple make their lines so perfect?
I'm using a CALayer and the Core Graphics API to draw the image on the right. Is it possible to draw such perfect lines with the standard apis?
The problem with drawing a 1-pixel path is that Quartz draws paths on an exact point grid, starting from {0,0}. This means that if you stroke a vertical path starting at {10,10} with a 1-point width, half of that line will render in the pixel to the left of the coordinate and half in the pixel to the right, causing a blurring effect.
You should therefore shift your drawing by {0.5,0.5} if you want lines to draw on exact pixels.
You can definitely draw what you want with Quartz.
Apple uses images for the tab elements.