fragment shader skips part of coding - python-3.x

Question

hi when i made my fragment shader coding i use:
---fragment
$HEADER$
void main(void)
{
float width = 0.0;
float offset = 0.1;
vec4 out_color = vec4(0, 0, 1, 1);
float coord = normalize(gl_FragCoord.x);
if (width == 0.0) {
vec4 out_color = vec4(0, 1, 1, 1);
}
else if (mod(((coord+offset) / width),2.0) < 0.3) {
vec4 out_color = vec4(0, 0, 0, 1);
}
gl_FragColor = out_color;
}
but when running the file with the vertex shader:
---vertex
$HEADER$
void main(void)
{
vec4 pos = vec4(vPosition.xy, 0.0, 1.0);
gl_Position = projection_mat * modelview_mat * pos;
}
and the python code:
from kivy.app import App
from kivy.base import EventLoop
from kivy.graphics import Mesh
from kivy.graphics.instructions import RenderContext
from kivy.uix.widget import Widged
w = 1000
h = 600
class GlslDemo(Widget):
def __init__(self, **kwargs):
Widget.__init__(self, **kwargs)
self.canvas = RenderContext(use_parent_projection=True)
self.canvas.shader.source = 'basic.glsl'
fmt = (
(b'vPosition', 2, 'float'),
)
vertices = (
0, 0,
w, 0,
w, h,
0, h,
)
indices = (0, 1, 2, 2, 3, 0)
with self.canvas:
Mesh(fmt=fmt, mode='triangles',
indices=indices, vertices=vertices)
class GlslApp(App):
def build(self):
EventLoop.ensure_window()
return GlslDemo()
if __name__ == '__main__':
GlslApp().run()
The problem when running this file is that it just outputs the vec4 out_color and skips the if and if else statements of the fragment shader code.

Answer 1

The variable out_color is declared 3 times in the fragment shader
1st in the scope of main
vec4 out_color = vec4(0, 0, 1, 1);
And another 2 times in the if statement:
if (width == 0.0) {
vec4 out_color = vec4(0, 1, 1, 1);
}
else if (mod(((coord+offset) / width),2.0) < 0.3) {
vec4 out_color = vec4(0, 0, 0, 1);
}
You have to assign to the variable which is declared in the scope of main, instead of declaring new variables in the if statement:
vec4 out_color = vec4(0, 0, 1, 1);
if (width == 0.0) {
out_color = vec4(0, 1, 1, 1);
}
else if (mod(((coord+offset) / width),2.0) < 0.3) {
out_color = vec4(0, 0, 0, 1);
}
Note, vec4 out_color; is a variable declaration, So vec4 out_color = vec4(0, 1, 1, 1); is an assignment to a new variabel, while out_color = vec4(0, 1, 1, 1); would assign to the existing variable out_color.