Matrix4 Multiply

Description

Multiplies one mat4 by another and copies the contents into a result mat4. Note that the function uses a temporary mat4 to hold values, so the destination matrix can be either one of the first two argument.

For instance if you wanted to multiply mat4 a, by mat4 b and store the results back in mat4 a, you would simply write.

mat4 a, b;
...
mat4_multiply(a, b, a);

Arguments

• mat4 a - factor
• mat4 b - factor
• mat4 dst - product

Source

void mat4_multiply(mat4 a, mat4 b, mat4 dst) {
	
    mat4 tmp;

    tmp[M_00] = a[M_00]*b[M_00]+a[M_01]*b[M_10]+a[M_02]*b[M_20]+a[M_03]*b[M_30];
    tmp[M_01] = a[M_00]*b[M_01]+a[M_01]*b[M_11]+a[M_02]*b[M_21]+a[M_03]*b[M_31];
    tmp[M_02] = a[M_00]*b[M_02]+a[M_01]*b[M_12]+a[M_02]*b[M_22]+a[M_03]*b[M_32];
    tmp[M_03] = a[M_00]*b[M_03]+a[M_01]*b[M_13]+a[M_02]*b[M_23]+a[M_03]*b[M_33];

    tmp[M_10] = a[M_10]*b[M_00]+a[M_11]*b[M_10]+a[M_12]*b[M_20]+a[M_13]*b[M_30];
    tmp[M_11] = a[M_10]*b[M_01]+a[M_11]*b[M_11]+a[M_12]*b[M_21]+a[M_13]*b[M_31];
    tmp[M_12] = a[M_10]*b[M_02]+a[M_11]*b[M_12]+a[M_12]*b[M_22]+a[M_13]*b[M_32];
    tmp[M_13] = a[M_10]*b[M_03]+a[M_11]*b[M_13]+a[M_12]*b[M_23]+a[M_13]*b[M_33];

    tmp[M_20] = a[M_20]*b[M_00]+a[M_21]*b[M_10]+a[M_22]*b[M_20]+a[M_23]*b[M_30];
    tmp[M_21] = a[M_20]*b[M_01]+a[M_21]*b[M_11]+a[M_22]*b[M_21]+a[M_23]*b[M_31];
    tmp[M_22] = a[M_20]*b[M_02]+a[M_21]*b[M_12]+a[M_22]*b[M_22]+a[M_23]*b[M_32];
    tmp[M_23] = a[M_20]*b[M_03]+a[M_21]*b[M_13]+a[M_22]*b[M_23]+a[M_23]*b[M_33];

    tmp[M_30] = a[M_30]*b[M_00]+a[M_31]*b[M_10]+a[M_32]*b[M_20]+a[M_33]*b[M_30];
    tmp[M_31] = a[M_30]*b[M_01]+a[M_31]*b[M_11]+a[M_32]*b[M_21]+a[M_33]*b[M_31];
    tmp[M_32] = a[M_30]*b[M_02]+a[M_31]*b[M_12]+a[M_32]*b[M_22]+a[M_33]*b[M_32];
    tmp[M_33] = a[M_30]*b[M_03]+a[M_31]*b[M_13]+a[M_32]*b[M_23]+a[M_33]*b[M_33];

    mat4_copy(tmp, dst);

}