Initial mask-image implementation https://files.facepunch.com/alexguthrie/1b1711b1/sbox_YDcpSIrUj9.png Mask-mode property, supports luminance & alpha New mask-image tests Apply css mask in panel layers https://files.facepunch.com/alexguthrie/1b1811b1/sbox_T4K1fa32Po.png Tests for mask-position, mask-size Basic mask-size, mask-position support, use custom alpha texture for tests We handle proper defaults for mask-size and mask-position, so no need to hack around it MaskAngle, convert to radians properly after parsing angles Use dict for angle direction LUT (easier to read) Fix RotateTexCoord not rotating correctly when given radians as input Simpler mask image test menu