Introducing 3D Graphics
PART ONE : TWO DIMENSIONAL TRANSFORMS
This is a preview version of something much better that Mr Pink is working on, which should appear in a future issue of Alive! - CiH
In the beginning there was the pixel. And the pixel begat the line and the sprite, and in turn these begat the polygon and texture mapped polygon. Whilst all you needed to create 2D games and demos was a basic grasp of algebra, 3D requires a greater knowledge base - trigonometry, vectors, matrix maths. All of this can appear somewhat daunting to the beginner.
The basic building blocks of 3D graphics are vectors. These are manipulated with matrices. It is by combining matrices and vectors that 3D scenes are made, and to be a good 3D coder you have to very comfortable maniuplating these elements.
To familarise yourself with vectors and matrices, I will present them in an environment you should be more familiar with - the world of 2D graphics.
VECTOR
A vector is a array of elements that can be used to represent points or the distance between points. For our 2D examples, the vector consists of just two elements, X and Y.
MATRIX
The matrix is used to manipulate vectors. For 2D graphics, a 3x2 matrix is used that is a matrix with 3 rows of two elements:
[ 00 ][ 01 ]
[ 10 ][ 11 ]
[ 20 ][ 21 ]In this matrix, the first two rows form the rotational/scaling component and the bottom row is the translation component.
The first column contains all the values that will affect the X element of the vector, and the second column has the values that will affect the Y component of the vector.
IDENTITY MATRIX
The identity matrix has the unique property that transforming a vector by it causes the original vector to be returned. Multiply another matrix by the identity matrix causes the original matrix to be returned - that is, transforming vectors and matrices by the identity matrix has no effect on their values. It is equivalent to multiplying a number by 1.
TRANSLATION MATRIX
A translation matrix translates a vector - that is it moves it around without altering its shape or scale.
To create a translation matrix, we just need to supply an x and y translation value.
SCALING MATRIX
A scaling matrix scales a vector. The scaling in the x and y dimensions can be specified separately and are totally independent.
ROTATION MATRIX
A rotation matrix rotates points around an axis.
We have created 3 different rotation matrices - one for each of the x,y and z axis. If we want to rotate an object using all three axis, we need to combine these 3 rotation matrices by multiplying them together.
APPENDIX A - DATA TYPES
typedef unsigned char U8;
typedef signed char S8;
typedef unsigned int U16;
typedef signed int S16;
typedef unsigned long U32;
typedef signed long S32;
typedef float F32;APPENDIX B - DATA STRUCTURES
typedef struct
{
F32 x;
F32 y;
} sVector2D;
typedef struct
{
F32 m[3][2];
} sMatrix2DAPPENDIX C - FUNCTIONS
void Matrix2D_TransformVector(sVector2D * apDest, sVector2D * apSrc, sMatrix2
{
apDest->x = (apSrc->x * aMat->m[0][0])
+ (apSrc->y * aMat->m[1][0])
+ aMat->m[2][0];
apDest->y = (apSrc->x * aMat->m[0][1])
+ (apSrc->y * aMat->m[1][1])
+ aMat->m[2][1];
}
void Matrix2D_Mul( sMatrix2D * apDst, sMatrix2D * apSrc0, sMatrix2D * apSrc1
{
U16 i,j;
for(i=0;i<2;i++)
{
for(j=0;j<2;j++)
{
apDst->m[i][j] = apSrc0->m[0][j] * apSrc1->m[i][0]
+ apSrc0->m[1][j] * apSrc1->m[i][1]
}
}
for(i=0;i<2;i++)
{
M[2][i] = apSrc0->m[0][i] * apSrc1->m[2][0]
+ apSrc0->m[1][i] * apSrc1->m[2][1]
+ apSrc0->m[2][i] * apSrc1->m[2][2]
+ apSrc0->m[3][i];
}
}
void Matrix2D_CreateIdentity( sMatrix2D * apMat )
{
apMat->m[ 0 ][ 0 ] = 1;
apMat->m[ 0 ][ 1 ] = 0;
apMat->m[ 1 ][ 0 ] = 0;
apMat->m[ 1 ][ 1 ] = 1;
apMat->m[ 2 ][ 0 ] = 0;
apMat->m[ 2 ][ 1 ] = 0;
}
void Matrix2D_CreateTranslation( sMatrix2D * apMat, F32 aX, F32 aY )
{
apMat->m[ 0 ][ 0 ] = 1;
apMat->m[ 0 ][ 1 ] = 0;
apMat->m[ 1 ][ 0 ] = 0;
apMat->m[ 1 ][ 1 ] = 1;
apMat->m[ 2 ][ 0 ] = aX;
apMat->m[ 2 ][ 1 ] = aY;
}
void Matrix2D_CreateScale( sMatrix2D * apMat, F32 aX, F32 aY )
{
apMat->m[ 0 ][ 0 ] = aX;
apMat->m[ 0 ][ 1 ] = 0;
apMat->m[ 1 ][ 0 ] = 0;
apMat->m[ 1 ][ 1 ] = aY;
apMat->m[ 2 ][ 0 ] = 0;
apMat->m[ 2 ][ 1 ] = 0;
}
void Matrix2D_CreateRotX( sMatrix2D * apMat, F32 aAngle )
{
apMat->m[ 0 ][ 0 ] = 1;
apMat->m[ 0 ][ 1 ] = 0;
apMat->m[ 1 ][ 0 ] = 0;
apMat->m[ 1 ][ 1 ] = 1;
apMat->m[ 2 ][ 0 ] = aX;
apMat->m[ 2 ][ 1 ] = aY;
}
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MrPink / RG
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