[raymath] MatrixMultiply multiplies matricies in wrong order #3039
Description
Test case comparing Raylib implementation to GLM:
#include <raylib.h>
#include <raymath.h>
#include <stdio.h>
#include "glm/mat4x4.hpp"
#include <glm/vec3.hpp> // glm::vec3
#include <glm/vec4.hpp> // glm::vec4
#include <glm/mat4x4.hpp> // glm::mat4
#include <glm/ext/matrix_transform.hpp> // glm::translate, glm::rotate, glm::scale
#include <glm/ext/matrix_clip_space.hpp> // glm::perspective
#include <glm/ext/scalar_constants.hpp> // glm::pi
void printMatrix(Matrix mat) {
printf("%.2f %.2f %.2f %.2f\n", mat.m0, mat.m4, mat.m8, mat.m12);
printf("%.2f %.2f %.2f %.2f\n", mat.m1, mat.m5, mat.m9, mat.m13);
printf("%.2f %.2f %.2f %.2f\n", mat.m2, mat.m6, mat.m10, mat.m14);
printf("%.2f %.2f %.2f %.2f\n", mat.m3, mat.m7, mat.m11, mat.m15);
printf("\n");
}
int main() {
struct Matrix view = MatrixLookAt((Vector3) {0.0f, 2.0f, 5.0f}, (Vector3) {1.0f, 20.0f, 1.0f}, (Vector3) {0.5f, 1.0f, 0.0f});
struct Matrix proj = MatrixPerspective(0.78f, 9.0f / 16.0f, 2.0f, 125.0f);
struct Matrix vipr = MatrixMultiply(view, proj);
struct Matrix vipr2 = MatrixMultiply(proj, view);
glm::mat4 Projection = glm::perspective(0.78f, 9.0f / 16.0f, 2.0f, 125.f);
glm::mat4 View = glm::lookAt(glm::vec3(0.0f, 2.0f, 5.0f), glm::vec3(1.0f, 20.0f, 1.0f), glm::vec3(0.5f, 1.0f, 0.0f));
glm::mat4 ViewProj = View * Projection;
printf("raylib: MatrixMultiply(view, proj)\n");
printMatrix(vipr);
printf("raylib: MatrixMultiply(proj, view)\n");
printMatrix(vipr2);
printf("glm: MatrixMultiply(view, proj), aka view * proj\n");
printf("%.2f %.2f %.2f %.2f\n", ViewProj[0][0], ViewProj[1][0], ViewProj[2][0], ViewProj[2][0]);
printf("%.2f %.2f %.2f %.2f\n", ViewProj[0][1], ViewProj[1][1], ViewProj[2][1], ViewProj[2][1]);
printf("%.2f %.2f %.2f %.2f\n", ViewProj[0][2], ViewProj[1][2], ViewProj[2][2], ViewProj[2][2]);
printf("%.2f %.2f %.2f %.2f\n", ViewProj[0][3], ViewProj[1][3], ViewProj[2][3], ViewProj[2][3]);
printf("\n");
}Test result
raylib: MatrixMultiply(view, proj)
1.89 -0.94 -3.78 20.76
2.18 0.11 1.06 -5.55
0.06 1.01 -0.22 -4.96
0.05 0.97 -0.22 -0.87
raylib: MatrixMultiply(proj, view)
1.89 -0.53 -3.90 3.55
3.88 0.11 1.83 -1.78
-0.23 -2.37 -1.09 -0.88
0.00 0.00 -1.00 0.00
glm: MatrixMultiply(view, proj), aka view * proj
1.89 -0.53 -3.90 -3.90
3.88 0.11 1.83 1.83
-0.23 -2.37 -1.09 -1.09
0.00 0.00 -1.00 -1.00
Produced result indicates that raylib's MatrixMultiply multiplies matrices right to left instead of left to right.
Possibly same issue in other functions that use matrix multiplication (i.e. Vector3Unproject)
I know it's a duplicate of #3036, but please, look at code I provided. It uses GLM, same print order, same operations.