How to redraw pixels on a 2DTexture without it flickering - unity3d

Question

I would like to draw a line on a 2DTexture within unity. This works well within the editor. However, in compiled builds it will flicker as it fills the pixels of the texture with clear colour then re-draws the line.
Here's my drawling code:
public void DrawLineWithMouse (Vector2 _middleVector)
{
tex.SetPixels(fillPixels); // Fills texture with an array of clear pixels
Vector3 newMousePos = Input.mousePosition;
newMousePos.z = 0;
int x0 = ((int)newMousePos.x)/RenderingManager.pixelSize / thickness; //Screen.width-
int y0 = ((int)newMousePos.y)/RenderingManager.pixelSize / thickness; //Screen.height-
int x1 = (int)_middleVector.x - (x0 - (int)_middleVector.x );
int y1 = (int)_middleVector.y - (y0 - (int)_middleVector.y );
DrawLineHelper(tex, x0, y0, x1, y1, Color.yellow); // redraws the line
tex.Apply();
}
I do not get flickering when I create a new texture then apply it. However, this is very, very expensive and for testing purposes only.
public void DrawLineWithMouse (Vector2 _middleVector)
{
tex = new Texture2D(Screen.width/RenderingManager.pixelSize / thickness, Screen.height/RenderingManager.pixelSize / thickness);
tex.SetPixels(fillPixels);
tex.SetPixels(fillPixels);
tex.filterMode = FilterMode.Point;
Vector3 newMousePos = Input.mousePosition;
newMousePos.z = 0;
int x0 = ((int)newMousePos.x)/RenderingManager.pixelSize / thickness; //Screen.width-
int y0 = ((int)newMousePos.y)/RenderingManager.pixelSize / thickness; //Screen.height-
int x1 = (int)_middleVector.x - (x0 - (int)_middleVector.x );
int y1 = (int)_middleVector.y - (y0 - (int)_middleVector.y );
DrawLineHelper(tex, x0, y0, x1, y1, Color.yellow);
GetComponent<Renderer>().material.mainTexture = tex;

Answer 1

It's flicking because apply is an expensive operation. The documentation states:
This is a potentially expensive operation, so you'll want to change as many pixels as possible between Apply calls.
You have to find a way to do less calls to DrawLineWithMouse. What's the best solution, that's up to you and depends on what you are doing.
One alternative is to accumulate deltas of mouse movement and draw after x milliseconds. Another alternative is to draw a mesh on top of the texture instead of changing the texture, and then only change the texture when necessary, if ever (note that you can use a RenderTexture here to easily draw the mesh in the texture).
Finally, lowering the resolution of the texture makes Apply run faster.