---
title: Sharing texture data between the Model I/O framework and the vImage library
framework: accelerate
role: sampleCode
role_heading: Sample Code
path: sample-code/accelerate/sharing-texture-data-between-the-model-io-framework-and-the-vimage-library
---

# Sharing texture data between the Model I/O framework and the vImage library

Use Model I/O and vImage to composite a photograph over a computer-generated sky.

## Overview

Overview The Model I/O framework provides the MDLTexture class and its subclasses to generate procedural textures such as noise, normal maps, and realistic sky boxes.  This sample code project uses an MDLSkyCubeTexture instance to generate a physically realistic simulation of a sunlit sky. The code uses the generated sky image as the background and a photograph of a building as the foreground. The image below shows the final composition:

Using the UI, someone can define the parameters that control the sky simulation such as upper atmosphere scattering and sun elevation. Before exploring the code, try building and running the app to get familiar with the effect of the different parameters on the image. Create the sky texture generator The ImageProvider class declares constants for the source image’s dimensions and the MDLSkyCubeTexture instance named skyGenerator: let width: Int var height: Int

let skyGenerator: MDLSkyCubeTexture The initializer creates the sky generator instance that’s the same size as the top layer image of the skyscraper: width = foregroundImage.width height = foregroundImage.height

skyGenerator = MDLSkyCubeTexture(name: nil,                                  channelEncoding: .uInt8,                                  textureDimensions: .init(x: Int32(width),                                                           y: Int32(height)),                                  turbidity: 0,                                  sunElevation: 0,                                  upperAtmosphereScattering: 0,                                  groundAlbedo: 0) Update the sky texture generator parameters With each change to the SwiftUI Picker controls that define the sky generator parameters, the app calls the renderSky() function. The function sets the sky generator parameters and calls update() to generate new texel data: skyGenerator.turbidity = turbidity skyGenerator.sunElevation = sunElevation skyGenerator.upperAtmosphereScattering = upperAtmosphereScattering skyGenerator.groundAlbedo = groundAlbedo

skyGenerator.update() Create the composite image The texelDataWithTopLeftOrigin() method returns the sky generator’s image data organized such that its first pixel represents the top-left corner of the image. This layout matches the vImage.PixelBuffer layout. The code passes the texel data to the withUnsafeBytes(_:) function to work with the underlying bytes of the data’s contiguous storage. let img = skyGenerator.texelDataWithTopLeftOrigin()?.withUnsafeBytes { skyData in The MDLSkyCubeTexture instance generates a cube texture that’s represented as six sides, vertically stacked.

The code below calculates the range texels that correspond to the selected side (one of ["+X", "-X", "+Y", "-Y", "+Z", "-Z"]) and binds those to Pixel_8 values: let imageIndex = ImageProvider.views.firstIndex(of: view) ?? 0 let imagePixelCount = width * height * format.componentCount

let range = imageIndex * imagePixelCount ..< (imageIndex + 1) * imagePixelCount

let values = skyData.bindMemory(to: Pixel_8.self)[ range ] The code below creates a vImage.PixelBuffer structure from the values and, because the alphaComposite(_:topLayer:destination:) method expects ARGB data, permutes the channel order so that alpha channel is first: let buffer = vImage.PixelBuffer(pixelValues: values,                                 size: .init(width: width, height: height),                                 pixelFormat: vImage.Interleaved8x4.self)

buffer.permuteChannels(to: (3, 0, 1, 2), destination: buffer) Finally, the sample code project composites the skyscraper image, represented by foregroundBuffer, over the sky image and returns a CGImage instance that contains the result:     buffer.alphaComposite(.nonpremultiplied,                           topLayer: foregroundBuffer,                           destination: buffer)          return buffer.makeCGImage(cgImageFormat: format) } // Ends `skyGenerator.texelDataWithTopLeftOrigin()?.withUnsafeBytes`.

## See Also

### vImage Pixel Buffers

- [Using vImage pixel buffers to generate video effects](accelerate/using-vimage-pixel-buffers-to-generate-video-effects.md)
- [Applying tone curve adjustments to images](accelerate/applying-tone-curve-adjustments-to-images.md)
- [Adjusting the brightness and contrast of an image](accelerate/adjusting-the-brightness-and-contrast-of-an-image.md)
- [Adjusting the hue of an image](accelerate/adjusting-the-hue-of-an-image.md)
- [Calculating the dominant colors in an image](accelerate/calculating-the-dominant-colors-in-an-image.md)
- [vImage.PixelBuffer](accelerate/vimage/pixelbuffer.md)