Horizontal Lines in Shape

[BenSCR]

How can I make 'Horizontal Lines' within a Triangle (or any shape) like in the attached photo...

[c.pfaffenbichler]

»Horizontal«? 

And please post images on the Forum directly: 

You can create a Pattern, then to warp, rotate and otherwise transform it convert a Pattern Layer to a Smart Object and apply a Vector Mask to it. 

[c.pfaffenbichler]

[BenSCR]

How do I create the pattern of lines?

[c.pfaffenbichler]

[c.pfaffenbichler]

For a horizontal line pattern you can use a Selection that is only 1px wide.