IMAGE: (hopefully) fixed uv calculation to solve issue #403

vengi-voxel · Aug 5, 2024 · 0d484e0 · 0d484e0
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diff --git a/docs/CHANGELOG.md b/docs/CHANGELOG.md
@@ -12,6 +12,8 @@ Known [issues](https://github.com/vengi-voxel/vengi/issues?q=is%3Aissue+is%3Aope
 
 General:
 
+   - Fixed invalid uv coordinate handling when importing meshes to voxelize them
+
 ## 0.0.33 (2024-08-05)
 
 General:

diff --git a/src/modules/image/Image.cpp b/src/modules/image/Image.cpp
@@ -296,8 +296,8 @@ void Image::flipVerticalRGBA(uint8_t *pixels, int w, int h) {
 glm::ivec2 Image::pixels(const glm::vec2 &uv, TextureWrap wrapS, TextureWrap wrapT) const {
 	const float w = (float)width();
 	const float h = (float)height();
-	int xint = (int)glm::roundEven(uv.x * w);
-	int yint = height() - (int)glm::roundEven(uv.y * h);
+	int xint = (int)glm::floor(uv.x * w);
+	int yint = height() - 1 - (int)glm::floor(uv.y * h);
 	switch (wrapS) {
 	case TextureWrap::Repeat: {
 		xint %= width();
@@ -362,8 +362,10 @@ glm::vec2 Image::uv(int x, int y) const {
 // | | | (pixel space 0/1 and 1/1), uv 0.25/0.25 and 0.75/0.25
 // -----
 glm::vec2 Image::uv(int x, int y, int w, int h) {
-	// sample the upper left corner of the pixel
-	return glm::vec2((float)x / (float)w, 1.0f - ((float)y / (float)h));
+	// Calculate the UV coordinates to sample the center of the pixel
+	float u = ((float)x + 0.5f) / (float)w;
+	float v = ((float)h - 1.0f - (float)y + 0.5f) / (float)h;
+	return glm::vec2(u, v);
 }
 
 bool Image::resize(int w, int h) {

diff --git a/src/modules/image/tests/ImageTest.cpp b/src/modules/image/tests/ImageTest.cpp
@@ -98,12 +98,17 @@ TEST_F(ImageTest, testGet) {
 	EXPECT_EQ(rgba, expected) << image::print(img);
 }
 
+TEST_F(ImageTest, testUV) {
+	EXPECT_VEC_NEAR(glm::vec2(0.001953f, 0.5f), image::Image::uv(0, 0, 256, 1), 0.000001f) << "lower left corner of the image";
+	EXPECT_VEC_NEAR(glm::vec2(0.75, 0.25f), image::Image::uv(1, 1, 2, 2), 0.000001f) << "lower left corner of the image";
+}
+
 TEST_F(ImageTest, testUVPixelBoundaries) {
 	const image::ImagePtr& img = image::loadImage("test-palette-in.png");
-	EXPECT_EQ(glm::vec2(0.0f, 0.0f), img->uv(0, img->height())) << "lower left corner of the image";
-	EXPECT_EQ(glm::vec2(1.0f, 0.0f), img->uv(img->width(), img->height())) << "lower right corner of the image";
-	EXPECT_EQ(glm::vec2(1.0f, 1.0f), img->uv(img->width(), 0)) << "upper right corner of the image";
-	EXPECT_EQ(glm::vec2(0.0f, 1.0f), img->uv(0, 0)) << "upper left corner of the image";
+	EXPECT_VEC_NEAR(glm::vec2(0.0119048f, 0.0067568f), img->uv(0, img->height() - 1), 0.000001f) << "lower left corner of the image (w: " << img->width() << ", h: " << img->height() << ")";
+	EXPECT_VEC_NEAR(glm::vec2(0.9880952f, 0.0067568f), img->uv(img->width() - 1, img->height() - 1), 0.000001f) << "lower right corner of the image (w: " << img->width() << ", h: " << img->height() << ")";
+	EXPECT_VEC_NEAR(glm::vec2(0.9880952f, 0.9932432f), img->uv(img->width() - 1, 0), 0.000001f) << "upper right corner of the image (w: " << img->width() << ", h: " << img->height() << ")";
+	EXPECT_VEC_NEAR(glm::vec2(0.0119048f, 0.9932432f), img->uv(0, 0), 0.000001f) << "upper left corner of the image (w: " << img->width() << ", h: " << img->height() << ")";
 }
 
 TEST_F(ImageTest, testUVPixelConversion) {

diff --git a/src/modules/voxelformat/private/mesh/MeshFormat.cpp b/src/modules/voxelformat/private/mesh/MeshFormat.cpp
@@ -136,8 +136,8 @@ glm::vec2 MeshFormat::paletteUV(int colorIndex) {
 	// 1 x 256 is the texture format that we are using for our palette
 	// sample the center of the palette pixels
 	// see https://github.com/vengi-voxel/vengi/issues/403
-	const float u = ((float)colorIndex + 0.4f) / (float)palette::PaletteMaxColors;
-	const float v = 0.6f;
+	const float u = (((float)colorIndex) + 0.5f) / (float)palette::PaletteMaxColors;
+	const float v = 0.5f;
 	return {u, v};
 }