How do I add transparency with a shader in SceneKit?
I would like to have a transparent effect on the image, now I am just testing with a torus, but the shader doesn't seem to work with alpha. From what I understood from this thread ( Using Related Functions in Scenekit ) and this wiki link on transparency: ( http://en.wikibooks.org/wiki/GLSL_Programming/GLUT/Transparency ) is GLBlendFunc
replaced with pragma transparency
in SceneKit.
Do you know what is wrong with this code?
I created a new project using SceneKit and I changed the ship's mesh for the torus.
EDIT:
I'm trying with a plane, but the image below doesn't appear inside the plane, instead I get an image with red and brownish rectangles below.
My image with alpha:
Result (the image with alpha should replace the brownish color):
let plane = SCNPlane(width: 2, height: 2)
var texture = SKTexture(imageNamed:"small")
texture.filteringMode = SKTextureFilteringMode.Nearest
plane.firstMaterial?.diffuse.contents = texture
let ship = SCNNode(geometry: plane) //SCNTorus(ringRadius: 1, pipeRadius: 0.5)
ship.position = SCNVector3(x: 0, y: 0, z: 15)
scene.rootNode.addChildNode(ship)
let myscale : CGFloat = 10
let box = SCNBox(width: myscale, height: myscale, length: myscale, chamferRadius: 0)
box.firstMaterial?.diffuse.contents = UIColor.redColor()
let theBox = SCNNode(geometry: box)
theBox.position = SCNVector3(x: 0, y: 0, z: 5)
scene.rootNode.addChildNode(theBox)
let scnView = self.view as SCNView
scnView.scene = scene
scnView.backgroundColor = UIColor.blackColor()
var shaders = NSMutableDictionary()
shaders[SCNShaderModifierEntryPointFragment] = String(contentsOfFile: NSBundle.mainBundle().pathForResource("test", ofType: "shader")!, encoding: NSUTF8StringEncoding, error: nil)
var material = SCNMaterial()
material.shaderModifiers = shaders
ship.geometry?.materials = [material]
Shader:
#pragma transparent
#pragma body
_output.color.rgba = vec4(0.0, 0.2, 0.0, 0.2);
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Adding transparency can easily be done at the insertion point of a SCNShadable
surface or fragment
Access point version SCNShaderModifierEntryPointSurface
#pragma transparent
#pragma body
_surface.diffuse.a = 0.5;
SCN entry point versionShaderModifierEntryPointFragment
#pragma transparent
#pragma body
_output.color.a = 0.5;
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I was struggling with this problem too. Finally I found out that for the C # pragma transparent to work, I had to add it in a different shader than the one my transparency code is doing.
For example, I added transparency code to the surface shader and added '#pragma transparent' to the geometry shader. Apple API doc also added "#pragma transparent" to geometry shader, don't know if they were designed for that.
NSString *geometryScript = @""
"#pragma transparent";
NSString *surfaceScript = @""
//"#pragma transparent" // You must not put it together with the transparency code
"float a = 0.1;"
"_surface.diffuse = vec4(_surface.diffuse.rgb * a, a);";
// This works for the transparency code in surface shader too.
//NSString *fragmentScript = @""
//"#pragma transparent";
yourMaterial.shaderModifiers = @{SCNShaderModifierEntryPointGeometry:geometryScript,
SCNShaderModifierEntryPointSurface:surfaceScript};
This code works in iOS 11.2, Xcode 9.2.
This rule also applies to the SCNShaderModifierEntryPointFragment shader. Likewise, if you want to change the transparency there, you can add '#pragma transparent' to the geometry or surface shader. I have not tested the SCNShaderModifierEntryPointLightingModel shader.
If you don't add "transparent" # pragma to the shader, the black background can be blended with transparent pixels.
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