Wireframe Shader For An SCNBox Geometry

MetalWireFrameShader.metal

/*
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ORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
*/


//------------------------
//MARK: - Transparent Body
//------------------------

float3 modelPosition = scn_node.modelTransform[3].xyz;
float3 viewPosition = scn_frame.inverseViewTransform[3].xyz;
float distance = length(modelPosition - viewPosition);

float3 bBoxMin = scn_node.boundingBox[0];
float3 bBoxMax = scn_node.boundingBox[1];
float3 size = bBoxMax - bBoxMin;
float bBoxDiag = length(size);

//-------------------------------
//MARK: - Render Only A Wireframe
//-------------------------------

float lineThickness = 0.02;
float u = _surface.diffuseTexcoord.x;
float v = _surface.diffuseTexcoord.y;

//-----------------------------------------
//MARK: - Compute Scaling Of Line Thickness
//-----------------------------------------

float2 scale;
if (abs((scn_node.inverseModelViewTransform * float4(_surface.normal, 0.0)).x) > 0.5) {
    scale = size.zy;
} else if (abs((scn_node.inverseModelViewTransform * float4(_surface.normal, 0.0)).y) > 0.5) {
    scale = size.xz;
} else {
    scale = size.xy;
}

//--------------------------------------------------
//MARK: - Compute Threshold For Discarding Rendering
//--------------------------------------------------

float2 thresh = float2(lineThickness) / scale;
if (u > thresh[0] && u < (1.0 - thresh[0]) && v > thresh[1] && v < (1.0 - thresh[1])) {
    discard_fragment();
}