diff --git a/src/cam.c b/src/cam.c
index c167032..85dec46 100644
--- a/src/cam.c
+++ b/src/cam.c
@@ -1,18 +1,18 @@
 #include "math/mat4.h"
-#include "math/vec3.h"
 #include "math/vec4.h"
 
 #include <math.h>
 
 Mat4f_t perspCam(float fov, float asp, float near, float far)
 {
-    const float t = 1 / tanf(fov/2);
+    const float t = 1.f / tanf(fov*0.5f);
+    const float fn = near - far;
     const float persp[16] = 
     {
         t/asp,  0.f, 0.f,                               0.f, 
         0.f,    t,   0.f,                               0.f,
-        0.f,    0.f, (far + near) / (far - near),       -1.f,
-        0.f,    0.f, (2.f * far * near) / (far - near), 0.f
+        0.f,    0.f, (far + near) / fn,                 -1.f,
+        0.f,    0.f, (2.f * far * near) / fn,           0.f
     };
 
     return mat4f_from_array(persp);
@@ -27,4 +27,10 @@ Vec4f_t* normCoord_r(Vec4f_t* vec)
     return vec;
 }
 
-// Vec3f_t 
\ No newline at end of file
+// first off, apply to your vec normCoord fn
+Vec4f_t* viewport_r(Vec4f_t* vec, float width, float height)
+{
+    vec->x = (vec->x + 1.f) * 0.5f * width;
+    vec->y = (1.f - vec->y) * 0.5f * height;
+    return vec;
+}
\ No newline at end of file
diff --git a/src/cam.h b/src/cam.h
index e69de29..f533b32 100644
--- a/src/cam.h
+++ b/src/cam.h
@@ -0,0 +1,6 @@
+#include "math/mat4.h"
+#include "math/vec4.h"
+
+Mat4f_t perspCam(float fov, float asp, float near, float far);
+Vec4f_t* normCoord_r(Vec4f_t* vec);
+Vec4f_t* viewport_r(Vec4f_t* vec, float width, float height);
\ No newline at end of file
diff --git a/src/main.c b/src/main.c
index b8cec70..90aa6ee 100644
--- a/src/main.c
+++ b/src/main.c
@@ -1,8 +1,38 @@
 #include <stdio.h>
-#include "math/mat4.h"
+#include "cam.h"
+#include "math/vec4.h"
+
+Vec4f_t mat4f_mul_vec4f(const Mat4f_t mat, Vec4f_t v)
+{
+    Vec4f_t out;
+    for (int i = 0; i < 4; i++)
+    {
+        out.data[i] = 0.f;
+        for (int j = 0; j < 4; j++)
+            out.data[i] += mat.m[i*4 + j] * v.data[j];
+    }
+    return out;
+}
 
 int main(int argc, const char** argv)
 {
-    printf("hello world");
+    const float fov = 60;
+    const float width = 1000, height = 800;
+    const float near = 0.1, far = 1000;
+
+    const float aspect = width / height;
+
+    // xyz = [-1, 1]
+    Vec4f_t vec = vec4f(0.f, 0.f, -1.f, 1.f);
+    Mat4f_t proj = perspCam(fov, aspect, near, far);
+
+    Vec4f_t v_clip = mat4f_mul_vec4f(proj, vec);
+
+    normCoord_r(&v_clip);
+    viewport_r(&v_clip, width, height);
+
+    printf("Screen coordinates: x = %f, y = %f, z = %f\n",
+        v_clip.x, v_clip.y, v_clip.z);
+
     return 0;
 }
\ No newline at end of file