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Need help understanding orthographic projection for UI rendering

None · 2020-05-12T14:34:55

I'm trying to create an orthographic projection using GLM for rendering UI elements. I have a window that's 1280x720 and I'm creating the projection like so: float aspect = (float) height / (float) width; // args: left, right, bottom, top, ... glm::mat4 projection = glm::ortho(-1.0, 1.0, -aspect, aspect , near, far); // near: -2.0, far: 2.0 If I create square mesh like this: auto geometry = Geometry::Primitive::Plane(1.0f, 1.0f * aspect); // (width, height) Then the square would look too wide, UNLESS I do this: auto geometry = Geometry::Primitive::Plane(1.0f * aspect, 1.0f * aspect); What do you all think I'm doing wrong, and what's the best way to construct an orthographic projection for rendering UI elements? Oh and one last thing: If my height is larger than my width, I'm guessing I would have to switch the division for my aspect ratio? Thanks all!

General and Gameplay Programming Programming

Started by EBZ May 12, 2020 05:04 AM

11 comments, last by EBZ 4 years, 1 month ago

Green_Baron

221

May 12, 2020 11:15 AM

There's no height/width ratio in the ortho matrix (pseudo-code, right handed, no depth version). it is simply a transform to a unit cube in the range -1/1 on all axes, oriented at the center:

mat4 ortho( left, right, bottom, top ) {
	mat4_t result = identity;
	result[0][0] = 2 / (right - left);
	result[1][1] = 2 / (top - bottom);
	result[2][2] = -1;
	result[3][0] = -(right + left) / (right - left);
	result[3][1] = -(top + bottom) / (top - bottom);
	return result;
}