debug - bad output

Drawing non-trivial line from p1(320.000, 80.000) to p2(360.000, 160.000)
stepping along the y axis starting with p1
drawing pixel at (-400, 80)
drawing pixel at (-398, 81)
drawing pixel at (-396, 82)
drawing pixel at (-394, 83)
drawing pixel at (-392, 84)
drawing pixel at (-390, 85)
drawing pixel at (-388, 86)
drawing pixel at (-386, 87)
drawing pixel at (-384, 88)
drawing pixel at (-382, 89)
drawing pixel at (-380, 90)
drawing pixel at (-378, 91)
drawing pixel at (-376, 92)
drawing pixel at (-374, 93)
drawing pixel at (-372, 94)
drawing pixel at (-370, 95)
drawing pixel at (-368, 96)
drawing pixel at (-366, 97)
drawing pixel at (-364, 98)
drawing pixel at (-362, 99)
drawing pixel at (-360, 100)
drawing pixel at (-358, 101)
drawing pixel at (-356, 102)
drawing pixel at (-354, 103)
drawing pixel at (-352, 104)
drawing pixel at (-350, 105)
drawing pixel at (-348, 106)
drawing pixel at (-346, 107)
drawing pixel at (-344, 108)
drawing pixel at (-342, 109)
drawing pixel at (-340, 110)
drawing pixel at (-338, 111)
drawing pixel at (-336, 112)
drawing pixel at (-334, 113)
drawing pixel at (-332, 114)
drawing pixel at (-330, 115)
drawing pixel at (-328, 116)
drawing pixel at (-326, 117)
drawing pixel at (-324, 118)
drawing pixel at (-322, 119)
drawing pixel at (-320, 120)
drawing pixel at (-318, 121)
drawing pixel at (-316, 122)
drawing pixel at (-314, 123)
drawing pixel at (-312, 124)
drawing pixel at (-310, 125)
drawing pixel at (-308, 126)
drawing pixel at (-306, 127)
drawing pixel at (-304, 128)
drawing pixel at (-302, 129)
drawing pixel at (-300, 130)
drawing pixel at (-298, 131)
drawing pixel at (-296, 132)
drawing pixel at (-294, 133)
drawing pixel at (-292, 134)
drawing pixel at (-290, 135)
drawing pixel at (-288, 136)
drawing pixel at (-286, 137)
drawing pixel at (-284, 138)
drawing pixel at (-282, 139)
drawing pixel at (-280, 140)
drawing pixel at (-278, 141)
drawing pixel at (-276, 142)
drawing pixel at (-274, 143)
drawing pixel at (-272, 144)
drawing pixel at (-270, 145)
drawing pixel at (-268, 146)
drawing pixel at (-266, 147)
drawing pixel at (-264, 148)
drawing pixel at (-262, 149)
drawing pixel at (-260, 150)
drawing pixel at (-258, 151)
drawing pixel at (-256, 152)
drawing pixel at (-254, 153)
drawing pixel at (-252, 154)
drawing pixel at (-250, 155)
drawing pixel at (-248, 156)
drawing pixel at (-246, 157)
drawing pixel at (-244, 158)
drawing pixel at (-242, 159)
drawing pixel at (-240, 160)