[Python] PyQtGraph: Custom Shader Not Displaying GLMeshItem

When importing ShaderProgram, VertexShader, and FragmentShader, I cannot get them to display my GLMeshItem.
I connect my shader to my GLMeshItem the way I see online in a very old forum:

gl.shaders.Shaders.append(ShaderProgram('hilight',
[
VertexShader("""
uniform mat4 u_mvp;
attribute vec4 a_position;
attribute vec3 a_normal;
attribute vec4 a_color;
varying vec4 v_color;
varying vec3 normal;
void main() {
// compute here for use in fragment shader
normal = normalize(gl_NormalMatrix * gl_Normal);
v_color = a_color;
gl_Position = u_mvp * a_position;
}
"""),
FragmentShader("""
#ifdef GL_ES
precision mediump float;
#endif
varying vec4 v_color;
varying vec3 normal;
void main() {
vec4 color = v_color;
color.x = (normal.x + 1.0) * 0.5;
color.y = (normal.y + 1.0) * 0.5;
color.z = (normal.z + 1.0) * 0.5;
gl_FragColor = color;
}
""")
]))


Then calling


self.current_plot = gl.GLMeshItem(
meshdata=mesh_data,
shader='hilight', # Set shader here
smooth=True,
drawFaces=True,
computeNormals=True
)


This fails but the same thing with shader='edgeHilight' (a built-in pyqtgraph shader) doesn't. Why? Even when 'hilight' is a carbon copy of 'edgeHilight', there is still no visual.
I made sure it was added to the list of shaders by calling

print("Shader program ID:", self.shader.program()) # Output 6


What's strange is that when I edit GLMeshItem's paint function like this:

def paint(self):
self.setupGLState()

self.parseMeshData()

if self.opts['drawFaces']:
with self.shader():
# Add debug lines
print("Position: " + str(glGetAttribLocation(self.shader().program(), 'a_position')))
print("Normal: " + str(glGetAttribLocation(self.shader().program(), 'a_normal')))
print("Color: " + str(glGetAttribLocation(self.shader().program(), 'a_color')))
# Rest of code...


With shader='hilight':

Position: 2
Normal: 0
Color: 1


but when shader='edgeHilight':

Position: -1
Normal: -1
Color: -1


This is counterintuitive since the latter is the shader that works.

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