Readme update - pictures made compatible with GitHub dark mode, added link to Atlas Gen, new example shader

README.md

@@ -10,12 +10,13 @@ to reproduce sharp corners almost perfectly by utilizing all three color channel
 
 The following comparison demonstrates the improvement in image quality.
 
-![demo-msdf16](https://user-images.githubusercontent.com/18639794/86908136-5fdd4780-c116-11ea-96c5-4f58a42043a4.png)
-![demo-sdf16](https://user-images.githubusercontent.com/18639794/86908146-6370ce80-c116-11ea-87ee-95bfb699665c.png)
-![demo-sdf32](https://user-images.githubusercontent.com/18639794/86908155-65d32880-c116-11ea-9583-1b45f806bbd9.png)
+![demo-msdf16](https://user-images.githubusercontent.com/18639794/106391899-e37ebe80-63ef-11eb-988b-4764004bb196.png)
+![demo-sdf16](https://user-images.githubusercontent.com/18639794/106391905-e679af00-63ef-11eb-96c3-993176330911.png)
+![demo-sdf32](https://user-images.githubusercontent.com/18639794/106391906-e7aadc00-63ef-11eb-8f84-d402d0dd9174.png)
 
 - To learn more about this method, you can read my [Master's thesis](https://github.com/Chlumsky/msdfgen/files/3050967/thesis.pdf).
-- Check what's new in the [changelog](CHANGELOG.md).
+- Check out my [MSDF-Atlas-Gen](https://github.com/Chlumsky/msdf-atlas-gen) if you want to generate entire glyph atlases for text rendering.
+- See what's new in the [changelog](CHANGELOG.md).
 
 ## Getting started
 
@@ -143,13 +144,12 @@ Using a multi-channel distance field generated by this program is similarly simp
 The only additional operation is computing the **median** of the three channels inside the fragment shader,
 right after sampling the distance field. This signed distance value can then be used the same way as usual.
 
-The following is an example GLSL fragment shader including anti-aliasing:
+The following is an example GLSL fragment shader with anti-aliasing:
 
 ```glsl
-in vec2 pos;
+in vec2 texCoord;
 out vec4 color;
 uniform sampler2D msdf;
-uniform float pxRange;
 uniform vec4 bgColor;
 uniform vec4 fgColor;
 
@@ -158,16 +158,35 @@ float median(float r, float g, float b) {
 }
 
 void main() {
-    vec2 msdfUnit = pxRange/vec2(textureSize(msdf, 0));
-    vec3 sample = texture(msdf, pos).rgb;
-    float sigDist = median(sample.r, sample.g, sample.b) - 0.5;
-    sigDist *= dot(msdfUnit, 0.5/fwidth(pos));
-    float opacity = clamp(sigDist + 0.5, 0.0, 1.0);
+    vec3 msd = texture(msdf, texCoord).rgb;
+    float sd = median(msd.r, msd.g, msd.b);
+    float screenPxDistance = screenPxRange()*(sd - 0.5);
+    float opacity = clamp(screenPxDistance + 0.5, 0.0, 1.0);
     color = mix(bgColor, fgColor, opacity);
 }
 ```
 
-**Note:** This is an example shader only and probably is not optimal for your use case! Please do not blindly copy & paste.
+Here, `screenPxRange()` represents the distance field range in output screen pixels. For example, if the pixel range was set to 2
+when generating a 32x32 distance field, and it is used to draw a quad that is 72x72 pixels on the screen,
+it should return 4.5 (because 72/32 * 2 = 4.5).
+**For 2D rendering, this can generally be replaced by a precomputed uniform value.**
+
+For rendering in a **3D perspective only**, where the texture scale varies across the screen,
+you may want to implement this function with fragment derivatives in the following way.
+I would suggest precomputing `unitRange` as a uniform variable instead of `pxRange` for better performance.
+
+```glsl
+uniform float pxRange; // set to distance field's pixel range
+
+float screenPxRange() {
+    vec2 unitRange = vec2(pxRange)/vec2(textureSize(msdf, 0));
+    vec2 screenTexSize = vec2(1.0)/fwidth(texCoord);
+    return max(0.5*dot(unitRange, screenTexSize), 1.0);
+}
+```
+
+`screenPxRange()` must never be lower than 1. If it is lower than 2, there is a high probability that the anti-aliasing will fail
+and you may want to re-generate your distance field with a wider range.
 
 ## Shape description syntax