First attempt at perspective correction

We inverse the perspective transformation to interpolate the scanlines.
The perspective is corrected but there are still precision problems (straight lines are deformed).

src/rendering/camera.c

@@ -183,6 +183,15 @@ CameraPerspective cameraGetPerspective(CameraDefinition* camera)
     return camera->perspective;
 }
 
+double cameraGetRealDepth(CameraDefinition* camera, Vector3 projected)
+{
+    /* TODO Optimize this */
+    Matrix4 m = m4NewPerspective(camera->perspective.yfov, camera->perspective.xratio, camera->perspective.znear, camera->perspective.zfar);
+    projected.x = (projected.x / (0.5 * camera->width) - 1.0);
+    projected.y = -(projected.y / (0.5 * camera->height) - 1.0);
+    return m4Transform(m4Inverse(m), projected).z;
+}
+
 void cameraSetLocation(CameraDefinition* camera, Vector3 location)
 {
     camera->location = location;

src/rendering/camera.h

@@ -35,6 +35,7 @@ Vector3 cameraGetDirection(CameraDefinition* camera);
 Vector3 cameraGetDirectionNormalized(CameraDefinition* camera);
 VectorSpherical cameraGetDirectionSpherical(CameraDefinition* camera);
 CameraPerspective cameraGetPerspective(CameraDefinition* camera);
+double cameraGetRealDepth(CameraDefinition* camera, Vector3 projected);
 
 void cameraSetLocation(CameraDefinition* camera, Vector3 location);
 void cameraSetLocationCoords(CameraDefinition* camera, double x, double y, double z);

src/rendering/render.c

@@ -5,6 +5,7 @@
 #include <math.h>
 
 #include "renderer.h"
+#include "camera.h"
 #include "system.h"
 
 typedef struct
@@ -381,10 +382,10 @@ static void _scanGetDiff(ScanPoint* v1, ScanPoint* v2, ScanPoint* result)
     result->callback = v1->callback;
 }
 
-static void _scanInterpolate(ScanPoint* v1, ScanPoint* diff, double value, ScanPoint* result)
+static void _scanInterpolate(CameraDefinition* camera, ScanPoint* v1, ScanPoint* diff, double value, ScanPoint* result)
 {
-    double v1depth = v1->pixel.z;
-    double v2depth = (v1->pixel.z + diff->pixel.z);
+    double v1depth = cameraGetRealDepth(camera, v1->pixel);
+    double v2depth = cameraGetRealDepth(camera, v3Add(v1->pixel, diff->pixel));
     double factor = ((1.0 - value) / v1depth + value / v2depth);
 
     result->pixel.x = v1->pixel.x + diff->pixel.x * value;
@@ -481,7 +482,7 @@ static void _pushScanLineEdge(RenderArea* area, ScanPoint* point1, ScanPoint* po
                 fx = point2->pixel.x;
             }
             fx = fx - point1->pixel.x;
-            _scanInterpolate(point1, &diff, fx / dx, &point);
+            _scanInterpolate(area->renderer->render_camera, point1, &diff, fx / dx, &point);
 
             /*point.pixel.x = (double)curx;*/
 
@@ -539,7 +540,7 @@ static void _renderScanLines(RenderArea* area)
                 fy = fy - down.pixel.y;
 
                 current.y = cury;
-                _scanInterpolate(&down, &diff, fy / dy, &current);
+                _scanInterpolate(area->renderer->render_camera, &down, &diff, fy / dy, &current);
 
                 _pushFragment(area, current.x, current.y, current.pixel.z, (cury == starty || cury == endy), current.location, current.callback);
             }

src/testing/test_camera.c

@@ -17,5 +17,41 @@ START_TEST(test_camera_definition)
 }
 END_TEST
 
-TEST_CASE(camera, test_camera_definition)
+START_TEST(test_camera_projection)
+{
+    CameraDefinition* cam;
+    cam = cameraCreateDefinition();
+
+    cameraSetLocationCoords(cam, 0.0, 1.0, 1.0);
+    cameraSetTargetCoords(cam, 0.0, 0.0, 0.0);
+
+    /* Test the reversibility of projection */
+    Vector3 point = cameraProject(cam, v3(12.0, 5.2, -6.3));
+    point = cameraUnproject(cam, point);
+    ck_assert_vector_values(point, 12.0, 5.2, -6.3);
+
+    cameraDeleteDefinition(cam);
+}
+END_TEST
+
+START_TEST(test_camera_depth)
+{
+    CameraDefinition* cam;
+    cam = cameraCreateDefinition();
+
+    cameraSetLocationCoords(cam, 0.0, 0.0, 0.0);
+    cameraSetTargetCoords(cam, 1.0, 0.0, 0.0);
+
+    /* Test the real depth getter */
+    Vector3 point = cameraProject(cam, v3(12.5, 0.0, 0.0));
+    ck_assert_double_eq(cameraGetRealDepth(cam, point), 12.5);
+
+    cameraDeleteDefinition(cam);
+}
+END_TEST
+
+TEST_CASE(camera,
+        test_camera_definition,
+        test_camera_projection,
+        test_camera_depth)