diff --git a/src/rendering/noise.c b/src/rendering/noise.c
index 60b652f..0baa57e 100644
--- a/src/rendering/noise.c
+++ b/src/rendering/noise.c
@@ -229,6 +229,13 @@ void noiseSetFunction(NoiseGenerator* generator, NoiseFunction* function)
     noiseValidate(generator);
 }
 
+void noiseSetCustomFunction(NoiseGenerator* generator, double (*func1d)(double x), double (*func2d)(double x, double y), double (*func3d)(double x, double y, double z))
+{
+    generator->_func_noise_1d = func1d;
+    generator->_func_noise_2d = func2d;
+    generator->_func_noise_3d = func3d;
+}
+
 void noiseSetFunctionParams(NoiseGenerator* generator, NoiseFunctionAlgorithm algorithm, double ridge_factor, double curve_factor)
 {
     NoiseFunction function = {algorithm, ridge_factor, curve_factor};
diff --git a/src/rendering/noise.h b/src/rendering/noise.h
index 5a30114..a8dea1a 100644
--- a/src/rendering/noise.h
+++ b/src/rendering/noise.h
@@ -46,6 +46,7 @@ void noiseCopy(NoiseGenerator* source, NoiseGenerator* destination);
 void noiseValidate(NoiseGenerator* generator);
 void noiseRandomizeOffsets(NoiseGenerator* generator);
 NoiseFunction noiseGetFunction(NoiseGenerator* generator);
+void noiseSetCustomFunction(NoiseGenerator* generator, double (*func1d)(double x), double (*func2d)(double x, double y), double (*func3d)(double x, double y, double z));
 void noiseSetFunction(NoiseGenerator* generator, NoiseFunction* function);
 void noiseSetFunctionParams(NoiseGenerator* generator, NoiseFunctionAlgorithm algorithm, double ridge_factor, double curve_factor);
 void noiseForceValue(NoiseGenerator* generator, double value);
diff --git a/src/testing/main.c b/src/testing/main.c
index 78b74d9..10ca434 100644
--- a/src/testing/main.c
+++ b/src/testing/main.c
@@ -7,6 +7,7 @@ extern void test_euclid_case(Suite* s);
 extern void test_camera_case(Suite* s);
 extern void test_clouds_case(Suite* s);
 extern void test_noise_case(Suite* s);
+extern void test_terrain_painting_case(Suite* s);
 
 int main(int argc, char** argv)
 {
@@ -20,6 +21,7 @@ int main(int argc, char** argv)
     test_camera_case(s);
     test_clouds_case(s);
     test_noise_case(s);
+    test_terrain_painting_case(s);
 
     SRunner *sr = srunner_create(s);
     srunner_run_all(sr, CK_NORMAL);
diff --git a/src/testing/test_terrain_painting.c b/src/testing/test_terrain_painting.c
new file mode 100644
index 0000000..c7750a7
--- /dev/null
+++ b/src/testing/test_terrain_painting.c
@@ -0,0 +1,95 @@
+#include "testing/common.h"
+
+#include <math.h>
+#include "rendering/tools.h"
+#include "rendering/terrain/public.h"
+
+/* Noise sin period is defined at 20.0 */
+#define X_FACTOR (M_PI / 10.0)
+
+static double _noise1dMock(double x)
+{
+    return sin(x * X_FACTOR) * 0.5 + 0.5;
+}
+
+static double _noise2dMock(double x, double y)
+{
+    UNUSED(y);
+    return sin(x * X_FACTOR) * 0.5 + 0.5;
+}
+
+static double _noise3dMock(double x, double y, double z)
+{
+    UNUSED(y);
+    UNUSED(z);
+    return sin(x * X_FACTOR) * 0.5 + 0.5;
+}
+
+static TerrainDefinition* _setUpDefinition()
+{
+    TerrainDefinition* terrain = (TerrainDefinition*)TerrainDefinitionClass.create();
+    terrain->height = 3.0;
+    terrain->scaling = 1.0;
+    noiseClearLevels(terrain->_height_noise);
+    NoiseLevel level = {1.0, 2.0, -1.0, 0.0, 0.0, 0.0};
+    noiseAddLevel(terrain->_height_noise, level, 0);
+    noiseSetCustomFunction(terrain->_height_noise, _noise1dMock, _noise2dMock, _noise3dMock);
+    return terrain;
+}
+
+static void _tearDownDefinition(TerrainDefinition* terrain)
+{
+    TerrainDefinitionClass.destroy(terrain);
+}
+
+START_TEST(test_terrain_painting_grid)
+{
+    /* Set up */
+    TerrainDefinition* terrain = _setUpDefinition();
+
+    /* Test base grid */
+    ck_assert_double_eq(terrainGetGridHeight(terrain, 0, 0, 0), 0.0);
+    ck_assert_double_eq(terrainGetGridHeight(terrain, 0, 1, 0), 0.0);
+    ck_assert_double_eq(terrainGetGridHeight(terrain, 0, 0, 1), 0.0);
+    ck_assert_double_eq(terrainGetGridHeight(terrain, 1, 0, 0), sin(1.0 * X_FACTOR));
+    ck_assert_double_eq(terrainGetGridHeight(terrain, 2, 0, 0), sin(2.0 * X_FACTOR));
+    ck_assert_double_eq(terrainGetGridHeight(terrain, 3, 0, 0), sin(3.0 * X_FACTOR));
+    ck_assert_double_eq(terrainGetGridHeight(terrain, 4, 0, 0), sin(4.0 * X_FACTOR));
+    ck_assert_double_eq(terrainGetGridHeight(terrain, 5, 0, 0), 1.0);
+    ck_assert_double_eq(terrainGetGridHeight(terrain, 6, 0, 0), sin(4.0 * X_FACTOR));
+    ck_assert_double_eq(terrainGetGridHeight(terrain, -1, 0, 0), -sin(1.0 * X_FACTOR));
+    ck_assert_double_eq(terrainGetGridHeight(terrain, 10, 0, 0), 0.0);
+    ck_assert_double_eq(terrainGetGridHeight(terrain, 15, 0, 0), -1.0);
+    ck_assert_double_eq(terrainGetGridHeight(terrain, 20, 0, 0), 0.0);
+    ck_assert_double_eq(terrainGetGridHeight(terrain, -5, 0, 0), -1.0);
+
+    /* Test interpolated result */
+    ck_assert_double_eq(terrainGetInterpolatedHeight(terrain, 0.0, 0.0, 0, 0), 0.0);
+    ck_assert_double_in_range(terrainGetInterpolatedHeight(terrain, 0.5, 0.0, 0, 0), 0.1564, 0.1566);
+    ck_assert_double_eq(terrainGetInterpolatedHeight(terrain, 1.0, 0.0, 0, 0), sin(1.0 * X_FACTOR));
+    ck_assert_double_eq(terrainGetInterpolatedHeight(terrain, 0.0, 0.0, 1, 0), 0.0);
+    ck_assert_double_in_range(terrainGetInterpolatedHeight(terrain, 0.5, 0.0, 1, 0), 3.0 * 0.1564, 3.0 * 0.1566);
+    ck_assert_double_eq(terrainGetInterpolatedHeight(terrain, 1.0, 0.0, 1, 0), 3.0 * sin(1.0 * X_FACTOR));
+
+    /* Test scaling */
+    terrain->scaling = 2.0;
+    ck_assert_double_eq(terrainGetGridHeight(terrain, 0, 0, 0), 0.0);
+    ck_assert_double_eq(terrainGetGridHeight(terrain, 1, 0, 0), sin(1.0 * X_FACTOR));
+    ck_assert_double_eq(terrainGetGridHeight(terrain, 2, 0, 0), sin(2.0 * X_FACTOR));
+    ck_assert_double_eq(terrainGetGridHeight(terrain, 3, 0, 0), sin(3.0 * X_FACTOR));
+    ck_assert_double_eq(terrainGetInterpolatedHeight(terrain, 0, 0, 0, 0), 0.0);
+    ck_assert_double_eq(terrainGetInterpolatedHeight(terrain, 1, 0, 0, 0), sin(0.5 * X_FACTOR));
+    ck_assert_double_eq(terrainGetInterpolatedHeight(terrain, 2, 0, 0, 0), sin(1.0 * X_FACTOR));
+    ck_assert_double_eq(terrainGetInterpolatedHeight(terrain, 3, 0, 0, 0), sin(1.5 * X_FACTOR));
+    ck_assert_double_eq(terrainGetInterpolatedHeight(terrain, 0, 0, 1, 0), 0.0);
+    ck_assert_double_eq(terrainGetInterpolatedHeight(terrain, 1, 0, 1, 0), 6.0 * sin(0.5 * X_FACTOR));
+    ck_assert_double_eq(terrainGetInterpolatedHeight(terrain, 2, 0, 1, 0), 6.0 * sin(1.0 * X_FACTOR));
+    ck_assert_double_eq(terrainGetInterpolatedHeight(terrain, 3, 0, 1, 0), 6.0 * sin(1.5 * X_FACTOR));
+
+    /* Tear down */
+    _tearDownDefinition(terrain);
+}
+END_TEST
+
+TEST_CASE(terrain_painting, test_terrain_painting_grid)
+