CODEWITHSUNDEEP
webgl
oceanGermanique
oceanGermanique

Reputation: 409

screen coordinates of a vertex with pointSize bigger than 1

assuming the canvas size is (wx,wy), the exact coordinates of the vertex lower and left is (-1 + 1/wx , -1 + 1/wy). But when the pointSize is bigger than 1, i dont managed to find a formula.

in this fiddle, https://jsfiddle.net/3u26rpf0/14/ i draw some pixels of size=1 with the following formula for gl_Position :

float p1 = -1.0 + (2.0 * a_position.x + 1.0) / wx ;  
float p2 = -1.0 + (2.0 * a_position.y + 1.0) / wy ;
gl_Position=vec4(p1,p2,0.0,1.0);

a_position.x goes from 0 to wx-1 .
a_position.y goes from 0 to wy-1 .

but if you change the value of size in the vertex (see fiddle link) my formula doesn't work, there is some offset to put.

Upvotes: 0

Views: 106

Answers (1)

user128511
user128511

Reputation:

From the OpenGL ES 2.0 spec section 3.3

Point rasterization produces a fragment for each framebuffer pixel whose center lies inside a square centered at the point’s (xw, yw), with side length equal to the point size

Upvotes: 2

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