$ gcc -o main -I. -I/usr/local/Cellar/sdl2/2.0.5/include -L/usr/local/Cellar/sdl2/2.0.5/lib main.c
In file included from main.c:7:
./transform.h:34:2: warning: implicit declaration of function 'settranslate' is invalid in C99
      [-Wimplicit-function-declaration]
        settranslate(&globaltransform, (double)halfscreenwidth, (double)halfscreenheight);
        ^
./transform.h:37:3: warning: implicit declaration of function 'setscale' is invalid in C99
      [-Wimplicit-function-declaration]
                setscale(&globaltransform, (double)(halfscreenwidth), (double)(-halfscreenwidth));
                ^
./transform.h:42:2: warning: implicit declaration of function 'setrotate' is invalid in C99
      [-Wimplicit-function-declaration]
        setrotate(&globaltransform, 0.0);
        ^
./transform.h:47:2: warning: implicit declaration of function 'settranslate3d' is invalid in C99
      [-Wimplicit-function-declaration]
        settranslate3d(&globaltransform3d, (double)halfscreenwidth, (double)halfscreenheight, 0.0);
        ^
./transform.h:50:3: warning: implicit declaration of function 'setscale3d' is invalid in C99
      [-Wimplicit-function-declaration]
                setscale3d(&globaltransform3d, (double)(halfscreenwidth), (double)(-halfscreenwidth), 1.0);
                ^
./transform.h:55:2: warning: implicit declaration of function 'setrotate3d' is invalid in C99
      [-Wimplicit-function-declaration]
        setrotate3d(&globaltransform, 0.0, 0.0, 0.0);
        ^
./transform.h:75:6: error: conflicting types for 'setscale'
void setscale(transform * t, double dx, double dy){
     ^
./transform.h:37:3: note: previous implicit declaration is here
                setscale(&globaltransform, (double)(halfscreenwidth), (double)(-halfscreenwidth));
                ^
./transform.h:85:6: error: conflicting types for 'settranslate'
void settranslate(transform * t, double dx, double dy){
     ^
./transform.h:34:2: note: previous implicit declaration is here
        settranslate(&globaltransform, (double)halfscreenwidth, (double)halfscreenheight);
        ^
./transform.h:96:6: error: conflicting types for 'setrotate'
void setrotate(transform * t, double a){
     ^
./transform.h:42:2: note: previous implicit declaration is here
        setrotate(&globaltransform, 0.0);
        ^
./transform.h:107:6: error: conflicting types for 'setscale3d'
void setscale3d(transform3d * t, double dx, double dy, double dz){
     ^
./transform.h:50:3: note: previous implicit declaration is here
                setscale3d(&globaltransform3d, (double)(halfscreenwidth), (double)(-halfscreenwidth), 1.0);
                ^
./transform.h:119:6: error: conflicting types for 'settranslate3d'
void settranslate3d(transform3d * t, double dx, double dy, double dz){
     ^
./transform.h:47:2: note: previous implicit declaration is here
        settranslate3d(&globaltransform3d, (double)halfscreenwidth, (double)halfscreenheight, 0.0);
        ^
./transform.h:132:6: error: conflicting types for 'setrotate3d'
void setrotate3d(transform3d * t, double ax, double ay, double az){
     ^
./transform.h:55:2: note: previous implicit declaration is here
        setrotate3d(&globaltransform, 0.0, 0.0, 0.0);
        ^
./transform.h:254:2: warning: implicit declaration of function 'setpointtransform' is invalid in C99
      [-Wimplicit-function-declaration]
        setpointtransform(p, defaulttransform);
        ^
./transform.h:257:6: error: conflicting types for 'setpointtransform'
void setpointtransform(point * p, double sx, double sy, double a, double tx, double ty){
     ^
./transform.h:254:2: note: previous implicit declaration is here
        setpointtransform(p, defaulttransform);
        ^
./transform.h:339:2: warning: implicit declaration of function 'setlinetransform' is invalid in C99
      [-Wimplicit-function-declaration]
        setlinetransform(l, defaulttransform);
        ^
./transform.h:342:6: error: conflicting types for 'setlinetransform'
void setlinetransform(line * l, double sx, double sy, double a, double tx, double ty){
     ^
./transform.h:339:2: note: previous implicit declaration is here
        setlinetransform(l, defaulttransform);
        ^
./transform.h:435:2: warning: implicit declaration of function 'settriangletransform' is invalid in C99
      [-Wimplicit-function-declaration]
        settriangletransform(tri, defaulttransform);
        ^
./transform.h:438:6: error: conflicting types for 'settriangletransform'
void settriangletransform(triangle * tri, double sx, double sy, double a, double tx, double ty){
     ^
./transform.h:435:2: note: previous implicit declaration is here
        settriangletransform(tri, defaulttransform);
        ^
./transform.h:554:2: warning: implicit declaration of function 'setmeshtransform' is invalid in C99
      [-Wimplicit-function-declaration]
        setmeshtransform(m, defaulttransform);
        ^
./transform.h:557:6: error: conflicting types for 'setmeshtransform'
void setmeshtransform(mesh * m, double sx, double sy, double a, double tx, double ty){
     ^
./transform.h:554:2: note: previous implicit declaration is here
        setmeshtransform(m, defaulttransform);
        ^
main.c:64:3: warning: implicit declaration of function 'setclearcolor' is invalid in C99
      [-Wimplicit-function-declaration]
                setclearcolor(0,0,0);
                ^
main.c:65:9: warning: implicit declaration of function 'time' is invalid in C99
      [-Wimplicit-function-declaration]
                srand(time(0));
                      ^
main.c:74:2: warning: implicit declaration of function 'clear' is invalid in C99
      [-Wimplicit-function-declaration]
        clear();
        ^
main.c:76:2: warning: implicit declaration of function 'setcolor' is invalid in C99
      [-Wimplicit-function-declaration]
        setcolor(0, 255, 0);
        ^
main.c:86:4: warning: implicit declaration of function 'drawvec3' is invalid in C99
      [-Wimplicit-function-declaration]
                        drawvec3(v1);
                        ^
main.c:90:5: warning: implicit declaration of function 'drawlinevec3' is invalid in C99
      [-Wimplicit-function-declaration]
                                drawlinevec3(v1, v0);
                                ^
main.c:100:2: warning: implicit declaration of function 'flip' is invalid in C99
      [-Wimplicit-function-declaration]
        flip();
        ^
main.c:163:3: warning: implicit declaration of function 'updatemouse' is invalid in C99
      [-Wimplicit-function-declaration]
                updatemouse();
                ^
main.c:164:3: warning: implicit declaration of function 'setdt' is invalid in C99
      [-Wimplicit-function-declaration]
                setdt();
                ^
main.c:185:6: error: conflicting types for 'drawvec3'
void drawvec3(vec3 v){ //renders pixel
     ^
main.c:86:4: note: previous implicit declaration is here
                        drawvec3(v1);
                        ^
main.c:211:6: error: conflicting types for 'drawlinevec3'
void drawlinevec3(vec3 v1, vec3 v2){ //renders point line
     ^
main.c:90:5: note: previous implicit declaration is here
                                drawlinevec3(v1, v0);
                                ^
main.c:375:6: error: conflicting types for 'updatemouse'
void updatemouse(void){
     ^
main.c:163:3: note: previous implicit declaration is here
                updatemouse();
                ^
main.c:385:6: error: conflicting types for 'setdt'
void setdt(void){
     ^
main.c:164:3: note: previous implicit declaration is here
                setdt();
                ^
main.c:396:6: error: conflicting types for 'setcolor'
void setcolor(Uint8 r, Uint8 g, Uint8 b){
     ^
main.c:76:2: note: previous implicit declaration is here
        setcolor(0, 255, 0);
        ^
main.c:404:6: error: conflicting types for 'setclearcolor'
void setclearcolor(Uint8 r, Uint8 g, Uint8 b){
     ^
main.c:64:3: note: previous implicit declaration is here
                setclearcolor(0,0,0);
                ^
main.c:412:6: error: conflicting types for 'clear'
void clear(void){
     ^
main.c:74:2: note: previous implicit declaration is here
        clear();
        ^
main.c:418:6: error: conflicting types for 'flip'
void flip(void){
     ^
main.c:100:2: note: previous implicit declaration is here
        flip();
        ^
19 warnings and 18 errors generated.