Godot 3.1 telling me that lock() and get_pixel() are nonexistent functions - godot

Question

I'm attempting to generate a height map from a noise texture. As far as I understand, in order to call get_pixel() on an image in this context, the image must first be locked. However, when I attempt to run the program, it exits with the error: Invalid call. Nonexistent function 'lock' in base 'StreamTexture'.
If I attempt to run it without locking the image, I get the error: Invalid call. Nonexistent function 'get_pixel' in base 'StreamTexture'.
I am certain that the instructions that I am following are for the same version of Godot I am running (3.1), so why is the engine telling me that lock() and get_pixel() are nonexistent functions?
My code is here:
extends Spatial
var width
var height
var heightData = {}
var vertices = PoolVector3Array()
var drawMesh = Mesh.new()
func _ready():
var noiseTexture = load("res://noiseTexture.png")
width = noiseTexture.get_width()
height = noiseTexture.get_height()
noiseTexture.lock()
for x in range(0, width):
for y in range(0, height):
heightData[Vector2(x,y)] = noiseTexture.get_pixel(x,y).r
noiseTexture.unlock()
for x in range(0, width-1):
for y in range(0, height-1):
createQuad(x,y)
var surfTool = SurfaceTool.new()
surfTool.begin(Mesh.PRIMITIVE_TRIANGLES)
for i in vertices.size():
surfTool.add_vertex(vertices[i])
surfTool.commit(drawMesh)
$MeshInstance.mesh = drawMesh
func createQuad(x,y):
#First half
vertices.push_back(Vector3(x, heightData[Vector2(x,y)], -y))
vertices.push_back(Vector3(x, heightData[Vector2(x,y+1)], -y-1))
vertices.push_back(Vector3(x+1, heightData[Vector2(x+1,y+1)], -y-1))
#Second Half
vertices.push_back(Vector3(x, heightData[Vector2(x,y)], -y))
vertices.push_back(Vector3(x+1, heightData[Vector2(x+1,y+1)], -y-1))
vertices.push_back(Vector3(x+1, heightData[Vector2(x+1,y)], -y))
Any help is greatly appreciated.
EDIT - I have (tried) to implement the changes that were suggested in the comments (yet I still don't know what to do with the color variable) and have attached a screenshot of my resulting code, as well as some comments I have made to try and explain to myself why the process SHOULD be working (I think). It also shows my node structure, which is why I opted to display this as an image. However, when I try to run this, the program crashes with the error displayed.

Answer 1

Check the docs;
StreamTexture does not have the method lock.
I think the class you are looking to use is Image. The Texture class is typically intended for drawing on the screen or applying to a Material
var noiseImage = Image.new()
noiseImage.load("res://noiseTexture.png")
noiseImage.lock() # Lock the image here
var color = noiseImage.get_pixel(10, 10) # Replace with your height map population
PS:
Just to let you know, I had a lot of issues with memory usage here so make sure you test that also (C# has bad garbage collector though).
You might need to dispose of the image, surface tool, and array mesh (If you remove the terrain object) to maintain optimum performance.

Answer 2

I have run into similar issues with generating heightmap terrains.
nathanfranke is correct and his solution will work.
If you for some reason use an ImageTexture you can call get_data() on that to get the underlying Image. Then you call lock() on the Image just like nathan says in his answer.
Take care to check that your coordinates for get_pixel() are correct. You can set a breakpoint by clicking on the very left edge of the line of code.
I mention this because I was very frustrated until I realized that my coordinate calculations were all int which resulted in the sampled pixel always being at <0,0>.
Here is part of my code for sampling an image into the HeightMapShape.map_data for Bullet heightmap collisions:
var map_w = shape.map_width
var map_h = shape.map_depth
var img_w = img.get_width()
var img_h = img.get_height()
img.lock()
for y in range(0, map_h):
py = float(img_h) * (float(y) / float(map_h))
for x in range(0, map_w):
px = float(img_w) * (float(x) / float(map_w))
index = y * img_h + x
pix = img.get_pixel(px, py)
shp.map_data[index] = pix.r * heightmap_height + heightmap_offset