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Draw an arrow in opengl ES

1) I know the starting point of the arrow and I know the ending point.

I have no idea how to draw an arrow head. I am assuming the other two points of the head are at an angle of 45 degrees from the end point ...

Does anyone know the formulas required for this?

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2 answers


Wade gives a good answer for the OpenGL part of this question; I'll try to answer the vector math part. Here's some pseudo code from above:



Triangle GenerateArrowHead(vec2 p1, vec2 p2)
{
    // Compute the vector along the arrow direction
    vec2 v = Normalize(p2 - p1)

    // Compute two perpendicular vectors to v
    vec2 vPerp1 = vec2(-v.y, v.x)
    vec2 vPerp2 = vec2(v.y, -v.x)

    // Compute two half-way vectors
    vec2 v1 = Normalize(v + vPerp1)
    vec2 v2 = Normalize(v + vPerp2)

    Triangle tri;
    tri.a = p2;
    tri.b = p2 + ArrowHeadSize * v1;
    tri.c = p2 + ArrowHeadSize * v2;
    return tri;
}
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Why doesn't it work?

1) Draw a triangle for the head (this means drawing with GL_TRIANGLES, not drawing three line segments that form a triangle)



2) Draw a line segment extending from the midpoint of the base of the triangle.

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