# How should I fill a shape consisting of Bezier curves and straight lines?

I have been working on a graphics library for some time now and have gotten to the point where I have to draw Bezier and line based fonts. Up to this point I am stuck with this:

The green lines are the Bezier paths, and the white part is what gets rendered.

The code I use for Beziers is here. The one for lines is here. For those who don't know that is Lua.

Path rendering (lines) : 32 - 39 The algorithm is as follows:

1. Iterating from 0 to 1 at certain intervals
2. calculating the x and y with this formula: (1-index)^2*x1+2*(1-index)*index*x2+index^2*x3

Up to this point everything works fine. The green lines are generated using the path method.

The white part is rendered in a completely different way:

1. I get the x coordinates of the Beziers and lines at a particular Y, the put them into a table.
2. I iterate through the table and each time I encounter a point I change the value of state. In the same for loop is also check whether state is on. If it is, I draw a pixel to the screen.

To find the x values of a y, I use the getX method (line 46 in Bezier and line 31 in Line).

The code I use for the drawing itself is this one:

local xBuffer = {}
local state = false

for i=0,500 do
for k,v in pairs(beziers) do
a,b = v.getX(i)
if a then
xBuffer[round(a)] = 1
if b then
xBuffer[round(a)] = 1
end
end
end
for k,v in pairs(lines) do
a = v.getX(i)
if a then
xBuffer[round(a)] = 1
end
end
state = false
for x=0,600 do
if xBuffer[x] then
state = not state
end
if state then
love.graphics.points(x,i)
end
end
end


Quick explanation: for i,v in pairs iterates through the table given as an argument to pairs. love.graphics.points(x,y) sets a point at x,y.

• Is there a reason nobody responds? Should I reformulate the question? – Creator Jan 12 '16 at 8:36
• Its early days there are only so many people who have time to answer and you've only so far reached 5 views. This stackexchange is still an infant and has not got many users give it time. – joojaa Jan 12 '16 at 10:52
• OK. Thanks. I did not realize so little people were here. – Creator Jan 12 '16 at 12:10

Instead, tessellate your Beziers into line segments and then throw those into the polygon scan converter. I suggest just using (recursive) binary subdivision: i.e. the quadratic Bezier with control points, $(\overline {A} , \overline {B} , \overline {C})$ can be split into two Beziers, $(\overline {A} , \overline {D} , \overline {E})$ and $(\overline {E} , \overline {F} , \overline {C})$ where \begin{align*} & \overline {D}=\dfrac {\overline {A}+\overline {B}} {2}\\ & \overline {E} =\dfrac {\overline {A}+2\overline {B}+\overline {C}}{4}\\ & \overline {F}=\dfrac {\overline {B}+\overline {C}} {2} \end{align*} (which is also great if you only have fixed point maths).