I'm trying binding libgd library with Nim, but I'm facing a problem with
pointers.
My interface:
# https://libgd.github.io/manuals/2.2.5/files/gd-h.html#gdPoint
type
gdImagePtr* = ref object
type
gdPoint* = object
x*: int
y*: int
proc gdImageCreate*(width: int, height: int): gdImagePtr {.importc, dynlib:
"/usr/lib/libgd.so".}
proc gdImageDestroy*(im: gdImagePtr): void {.importc, dynlib:
"/usr/lib/libgd.so".}
#
# These functions mimic the original functions of the library and it is in
these functions that I have problems.
#
proc gdImagePolygon*(im: gdImagePtr, p: gdPointPtr, n: int, c: int): void
{.importc, dynlib: "/usr/lib/libgd.so".}
proc gdImageOpenPolygon*(im: gdImagePtr, p: gdPointPtr, n: int, c: int):
void {.importc, dynlib: "/usr/lib/libgd.so".}
proc gdImageFilledPolygon*(im: gdImagePtr, p: gdPointPtr, n: int, c: int):
void {.importc, dynlib: "/usr/lib/libgd.so".}
# I skipped many functions
template withGd*(img: untyped, width: int, height: int, body: untyped):
typed =
block gd:
let img = gdImageCreate(width, height)
body
gdImageDestroy(img)
Run
# Polygon
withGd im, 500, 500:
var points: array[4, gdPoint]
points[0].x = 50
points[0].y = 50
points[1].x = 250
points[1].y = 50
points[2].x = 250
points[2].y = 200
points[3].x = 50
points[3].y = 200
let white = im.color(255, 255, 255)
let red = im.color(255, 0, 0)
im.gdImagePolygon(addr points, points.len, red)
let png_out = open("outputs/test_polygon.png", fmWrite)
im.save(png_out, extension="png")
png_out.close()
Run
I need to pass a pointer to the array of points. So I replace gdImagePtr with
pointer type.
# Original
proc gdImagePolygon*(im: gdImagePtr, p: gdPointPtr, n: int, c: int): void
{.importc, dynlib: "/usr/lib/libgd.so".}
# I replace the gdPointPtr with pointer type
proc gdImagePolygon*(im: gdImagePtr, p: pointer, n: int, c: int): void
{.importc, dynlib: "/usr/lib/libgd.so".}
Run
The code compiles, but does not draw the lines properly, only one line appears
at the top. What is wrong?
