Calculating sprite coords in sprite sheet texture ?

Graphics and GPU Programming Programming OpenGL

Started by vNeeki March 24, 2012 01:33 PM

3 comments, last by vNeeki 12 years ago

194

Author

March 24, 2012 01:33 PM

I have created a small sprite sheet(64x256) with all the frames of an animated sprite(64x64 each) , and im uploading that
texture into opengl in order to avoid binds for each animation state change.

But im facing a little problem with the mapping , and particurarly with the texture coordinates.
When i attempt to map anything but the first i simply get random parts of the frame rendered.

This is how i calculate my coords :



void CalculateCoordsForQuad(vector<Vector2F>& coords,const Vector2F& frame_position,const Vector2F& frame_dimensions,

const Vector2F& sprite_sheet_dimensions)

{

	//Calculate offset of sprite in sprite sheet

	float x1 = frame_position.X / sprite_sheet_dimensions.X;

	float x2 = (frame_position.X + frame_dimensions.X) / sprite_sheet_dimensions.X;

	float y1 = frame_position.Y / sprite_sheet_dimensions.Y;

	float y2 = (frame_position.Y + frame_dimensions.Y) / sprite_sheet_dimensions.Y;



	//Map Quad coordinates (2 GL_TRIANGLES)

	coords.clear();



	//Triangle 1

	coords.push_back(Vector2F(x1,y1));

	coords.push_back(Vector2F(x2,x1));

	coords.push_back(Vector2F(y1,y2));



    //Triangle 2

	coords.push_back(Vector2F(x1,y2));

	coords.push_back(Vector2F(x2,y1));

	coords.push_back(Vector2F(x2,y2));

}

And how i display them :



vector<Vector2F> coords;

const Vector2F first_frame(0,0);

const Vector2F second_frame(64,0);

const Vector2F frame_dim(64,64);

const Vector2F sheet_dim(256,64);



CalculateCoordsForQuad(coords,second_frame,frame_dim,sheet_dim);



//Now map + upload vertices with immediate mode

But like i mentioned already it will only display correctly the first sprite which is frustrating.

...Anyone seeing anything wrong with my math ?

slicer4ever

6,773

March 25, 2012 12:00 AM

your math looks good, your x1/x2 should be 0.25/0.5, and y1/y2 should be 0.0/1.0. what are you getting when u look what is written into coords?

also, can we see how the image is uploaded, and how your drawing it.

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vNeeki

194

Author

March 25, 2012 08:41 AM

Thanks.

I think that the problem is with the way im mapping the triangle(i got it to work with deprecated GL_QUADS).
...Seems like i will have to play around with vertices a little more.

haegarr

7,408

March 25, 2012 08:51 AM

//Triangle 1 coords.push_back(Vector2F(x1,y1)); coords.push_back(Vector2F(x2,x1)); coords.push_back(Vector2F(y1,y2)); //Triangle 2 coords.push_back(Vector2F(x1,y2)); coords.push_back(Vector2F(x2,y1)); coords.push_back(Vector2F(x2,y2));

and then

I think that the problem is with the way im mapping the triangle(i got it to work with deprecated GL_QUADS).
...Seems like i will have to play around with vertices a little more.

GL_QUAD expects 4 vertices per quad. Hence you need 4 UV coordinate pairs. But you compute 6 pairs, because you handle the quad as 2 triangles.

haegarr

7,408

March 25, 2012 08:56 AM

...
//Triangle 1 coords.push_back(Vector2F(x1,y1)); coords.push_back(Vector2F(x2,x1)); coords.push_back(Vector2F(y1,y2));
...

At least: The 2nd UV pair consists of x co-ordinates only, and the 3rd pair of y co-ordinates.

vNeeki

194

Author

March 25, 2012 09:13 AM

[quote name='vNeeki' timestamp='1332595982' post='4924875']
...
//Triangle 1 coords.push_back(Vector2F(x1,y1)); coords.push_back(Vector2F(x2,x1)); coords.push_back(Vector2F(y1,y2));
...

At least: The 2nd UV pair consists of x co-ordinates only, and the 3rd pair of y co-ordinates.
[/quote]

Fixed it.Thank you !

Calculating sprite coords in sprite sheet texture ?

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Calculating sprite coords in sprite sheet texture ?

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