GTE beginner questions

[Jaberwocky]

Heyho

I started reading and playing around with the GTE - and as always I run into various problems. (I wonder why am I always the guy asking those things >o<)

My plan is to display a simple 2D rectangle with a texture, with all the GTE stuff happening but with a rotation and translation of 0 - also with no perspective. So Basicly I want to see my sprite.
The good thing is: I see my sprite ^o^ The bad thing... it is 2 times bigger then it should be and it refuses to shrink in size :/

My GTE setup code looks like that:

Code: Select all

VECTOR  transV{0, 0, 0};
SVECTOR rotV{0, 0, 0};

//We run in PAL mode
SetVideoMode(MODE_PAL);
SsSetTickMode(SS_TICK50);

/*
Setting up double buffer and such
*/

InitGeom();
SetGeomOffset(0, 0);
SetGeomScreen(512);

TransMatrix(&trans, &transV);
RotMatrix_gte(&rotV, &rot);


SetRotMatrix(&rot);
SetTransMatrix(&trans);

SetDispMask(0);

Before stuffing my "POLY_FT4" to the ordering table I do:

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SVECTOR inputCoordinates[] =
{
	this->position,
	{(this->position.vx + Flammie::Width),  this->position.vy,                    this->position.vz},
	{ this->position.vx,                   (this->position.vy + Flammie::Height), this->position.vz},
	{(this->position.vx + Flammie::Width), (this->position.vy + Flammie::Height), this->position.vz}
};

long p;
long flag;

RotAverage4(&inputCoordinates[0], &inputCoordinates[1], &inputCoordinates[2], &inputCoordinates[3],
		   (long*)&this->ouput.x0, (long*)&this->ouput.x1, (long*)&this->ouput.x2, (long*)&this->ouput.x3,
		    &p, &flag);

position is a SVECTOR set to {0, 0, 0} because I wanted the sprite to appear in the upper left corner. Which he does but 2 times his size.

I also tried applying a scaling vector in my setup phase - but no matter what I do it stays two times its size :/

Code: Select all

MATRIX  scaly;
VECTOR  scaleV{2048, 2048, 2048};

SetRotMatrix(&rot);
SetTransMatrix(&trans);
MulRotMatrix(&scaly);

Any ideas? >o<
Also... is there some explaining reading material to pick up on those subjects?

[Jaberwocky]

I actually made progress on this! I figured out, that when the Z Axis of my sprite is 0, then the it will be twice the original size.
So I set the Z to 1 and set the SetGeomScreen to 1. Now it works! I think this is related to the perspective calculation (h/Sz)? Where h is the distance to the screen.

However if I set SetGeomScreen to 512 while having Z at 1 - then my sprite is again two times the size... Why? I don't get that relation....

Edit: I bound the Z-Axis to L1 and R1 to play around a bit with it. Now I can kiiiinda see/guess the perspective that is used. Still a bit confusing though...