fixes

README.md

@@ -48,10 +48,6 @@ python convert.py equi.png --to_mercator
 
 You can use the Converter class directly in Python. Check out the [demo script](demo.py) to see how to run conversions from code.
 
-## Limitations
-
-The conversion process doesn't handle longitude angles of 85+ degress well. Converted images may display issues around the top and bottom borders.
-
 ## Python package
 
 If anyone wants to transform this into a functional, publishable package, feel free to fork the project and publish it. I don't have enough experience doing that and can't imagine many people will use this thing to make the extra effort worthwhile.

src/cpu_render.py

@@ -12,42 +12,27 @@ def clamp(value, minValue, maxValue):
 
 def equi_to_merc(u, v):
     # uv to equirectangular
-    lat = remap(u, 0, 1, 0, 2 * math.pi)
-    lon = remap(v, 0, 1, -math.pi * 0.5, math.pi * 0.5)
+    lon = remap(v, 0, 1, -MERC_MAX_LON, MERC_MAX_LON)
 
     # equirectangular to mercator
-    x = lat
-    lon = clamp(lon, -MERC_MAX_LON, MERC_MAX_LON)
     y = math.log(math.tan(math.pi / 4 + lon / 2))
 
     # mercator to uv
-    x = remap(x, 0, 2 * math.pi, 0, 1)
     y = remap(y, -math.pi, math.pi, 0, 1)
 
-    # clamp
-    x = clamp(x, 0, 1)
-    y = clamp(y, 0, 1)
-
-    return (x, y)
+    return (u, y)
 
 def merc_to_equi(u, v):
     # uv to mercator
-    lat = remap(u, 0, 1, 0, 2 * math.pi)
     lon = remap(v, 0, 1, -math.pi, math.pi)
 
     # mercator to equirectangular
-    x = lat
     y = 2 * math.atan(math.pow(math.e, lon)) - math.pi * 0.5
 
     # equirectangular to uv
-    x = remap(x, 0, 2 * math.pi, 0, 1)
-    y = remap(y, -math.pi * 0.5, math.pi * 0.5, 0, 1)
-
-    # clamp
-    x = clamp(x, 0, 1)
-    y = clamp(y, 0, 1)
+    y = remap(y, -MERC_MAX_LON, MERC_MAX_LON, 0, 1)
 
-    return (x, y)
+    return (u, y)
 
 def render(image: Image.Image, conversion: CONVERSION):
     if conversion == CONVERSION.TO_MERCATOR:
@@ -62,12 +47,19 @@ def render(image: Image.Image, conversion: CONVERSION):
     progress = 0
     for x in range(newImage.width):
         for y in range(newImage.height):
+            # Coordinate limits
+            maxX = newImage.width - 1
+            maxY = newImage.height - 1
+
+            # Conversion
             if conversion == CONVERSION.TO_MERCATOR:
                 # Running through a merc image, we need to sample equi
-                (u, v) = merc_to_equi(x / newImage.width, y / newImage.height)
+                (u, v) = merc_to_equi(x / maxX, y / maxY)
             else:
                 # Running through an equi image, we need to sample merc
-                (u, v) = equi_to_merc(x / newImage.width, y / newImage.height)
+                (u, v) = equi_to_merc(x / maxX, y / maxY)
+
+            # Resample original image using converted UVs
             sampleX = round(u * (image.width - 1))
             sampleY = round(v * (image.height - 1))
             newPixels[x, y] = pixels[sampleX, sampleY]

src/shaders/fragment_to_equirectangular.glsl

@@ -3,8 +3,9 @@ in vec2 fragCoord;
 out vec4 fragColor;
 uniform sampler2D texture;
 
-#define M_PI 3.1415926535897932384626433832795
-#define M_E 2.7182818284590452353602874713527
+#define M_PI 3.1415926535897932
+#define M_E 2.7182818284590452
+#define M_MAX 1.4844222297453324
 
 float remap(float value, float oldMin, float oldMax, float newMin, float newMax)
 {
@@ -14,18 +15,15 @@ float remap(float value, float oldMin, float oldMax, float newMin, float newMax)
 vec2 equi_to_merc(float u, float v)
 {
     // uv to equirectangular
-    float lat = remap(u, 0, 1, 0, 2 * M_PI);
-    float lon = remap(v, 0, 1, -M_PI * 0.5, M_PI * 0.5);
+    float lon = remap(v, 0, 1, -M_MAX, M_MAX);
 
     // equirectangular to mercator
-    float x = lat;
     float y = log(tan(M_PI / 4 + lon / 2));
 
     // mercator to uv
-    x = remap(x, 0, 2 * M_PI, 0, 1);
     y = remap(y, -M_PI, M_PI, 0, 1);
 
-    return vec2(x, y);
+    return vec2(u, y);
 }
 
 void main()

src/shaders/fragment_to_mercator.glsl

@@ -3,8 +3,9 @@ in vec2 fragCoord;
 out vec4 fragColor;
 uniform sampler2D texture;
 
-#define M_PI 3.1415926535897932384626433832795
-#define M_E 2.7182818284590452353602874713527
+#define M_PI 3.1415926535897932
+#define M_E 2.7182818284590452
+#define M_MAX 1.4844222297453324
 
 float remap(float value, float oldMin, float oldMax, float newMin, float newMax)
 {
@@ -14,18 +15,15 @@ float remap(float value, float oldMin, float oldMax, float newMin, float newMax)
 vec2 merc_to_equi(float u, float v)
 {
     // uv to mercator
-    float lat = remap(u, 0, 1, 0, 2 * M_PI);
     float lon = remap(v, 0, 1, -M_PI, M_PI);
 
     // mercator to equirectangular
-    float x = lat;
     float y = 2 * atan(pow(M_E, lon)) - M_PI * 0.5;
 
     // equirectangular to uv
-    x = remap(x, 0, 2 * M_PI, 0, 1);
-    y = remap(y, -M_PI * 0.5, M_PI * 0.5, 0, 1);
+    y = remap(y, -M_MAX, M_MAX, 0, 1);
 
-    return vec2(x, y);
+    return vec2(u, y);
 }
 
 void main()