Drawing a vertical line at cursor position

OpenGL OpenGL: Basic Coding
1

Hello!

I’m learning OpenGL so decided to make an application which draw plots. I decided to make a selection so found that drawing vertical line is slow.

I would like to draw a vertical line at a cursor’s position. The line moves as the cursor moves. The algorithm is:

1. Put data for 2 vertices (-1, 1, 0) and (-1, -1, 0) into array buffer for dynamic drawing.
2. Load shader which in fact just a white pixel.

loop:
	3. Catch mouse position.
	4. Update the coordinates of the vertieces.
	5. Bind the vertex array of the vertieces.
	6. Draw arrays in GL_LINES mode.
	7. Unbind.

The problem is that the line doesn’t stick to the cursor. It is drawn with some delay. For example if I select files in my file explorer I don’t see such delay of a selection rectangle so it sticks right to the cursor. I don’t see that in a real-time strategy game selecting unites. So here I don’t understand what slows down my application.

I removed everything leaving only drawing the line. Still there 214 lines. You can see the C code here.

If you decide to build it and launch, please notice that path to the shaders supposes the application to be launched from the root of the project.

2

I’ve found a possible solution of the issue. By default motion of a cursor is affected by scaling and acceleration. It is designated in the documentation of GLFW about GLFW_RAW_MOUSE_MOTION (unfortunately I can’t write a link due to forum’s rules). By now I got that it’s impossible to have a line sticked to a cursor. At least to a system cursor. Perhaps diving into the source code of glfw can give another conclusion.

Bottom line:
In order to draw a line which moves with a mouse you need to add the following code

    if (glfwRawMouseMotionSupported()) {
        glfwSetInputMode(window, GLFW_CURSOR, GLFW_CURSOR_DISABLED);
        glfwSetInputMode(window, GLFW_RAW_MOUSE_MOTION, GLFW_TRUE);
    } else {
        printf("glfwRawMouseMotionSupported is not\n");
    }

It disables drawing of a system cursor and disables acceleration and scaling of position of a cursor.

3

Glad you got it figured out. Here’s that link:

Re “can’t write a link”, just keep using the forums and those restrictions will evaporate on your account pretty quickly.