Fix MSAA stripes (#9247)

This only works when shaders are enabled.
The centroid varying avoids that the textures (which repeat themselves out of bounds) are sampled out of bounds in MSAA.
If MSAA (called FSAA in minetest) is disabled, the centroid keyword does nothing.

2 files changed, 8 insertions, 5 deletions

diff --git a/client/shaders/nodes_shader/opengl_fragment.glsl b/client/shaders/nodes_shader/opengl_fragment.glsl
index 82c87073a..b0f6d45d0 100644
--- a/client/shaders/nodes_shader/opengl_fragment.glsl
+++ b/client/shaders/nodes_shader/opengl_fragment.glsl
@@ -16,7 +16,7 @@ varying vec3 vPosition;
 // precision must be considered).
 varying vec3 worldPosition;
 varying lowp vec4 varColor;
-varying mediump vec2 varTexCoord;
+centroid varying mediump vec2 varTexCoord;
 varying vec3 eyeVec;
 
 const float fogStart = FOG_START;
@@ -46,7 +46,7 @@ vec4 applyToneMapping(vec4 color)
 	const float gamma = 1.6;
 	const float exposureBias = 5.5;
 	color.rgb = uncharted2Tonemap(exposureBias * color.rgb);
-	// Precalculated white_scale from 
+	// Precalculated white_scale from
 	//vec3 whiteScale = 1.0 / uncharted2Tonemap(vec3(W));
 	vec3 whiteScale = vec3(1.036015346);
 	color.rgb *= whiteScale;
@@ -72,7 +72,7 @@ void main(void)
 	color = base.rgb;
 
 	vec4 col = vec4(color.rgb * varColor.rgb, 1.0);
-	
+
 #ifdef ENABLE_TONE_MAPPING
 	col = applyToneMapping(col);
 #endif
diff --git a/client/shaders/nodes_shader/opengl_vertex.glsl b/client/shaders/nodes_shader/opengl_vertex.glsl
index cb344f6e6..5742ec1d3 100644
--- a/client/shaders/nodes_shader/opengl_vertex.glsl
+++ b/client/shaders/nodes_shader/opengl_vertex.glsl
@@ -16,7 +16,10 @@ varying vec3 vPosition;
 // precision must be considered).
 varying vec3 worldPosition;
 varying lowp vec4 varColor;
-varying mediump vec2 varTexCoord;
+// The centroid keyword ensures that after interpolation the texture coordinates
+// lie within the same bounds when MSAA is en- and disabled.
+// This fixes the stripes problem with nearest-neighbour textures and MSAA.
+centroid varying mediump vec2 varTexCoord;
 varying vec3 eyeVec;
 
 // Color of the light emitted by the light sources.
@@ -142,7 +145,7 @@ void main(void)
 	vec4 color;
 	// The alpha gives the ratio of sunlight in the incoming light.
 	float nightRatio = 1.0 - inVertexColor.a;
-	color.rgb = inVertexColor.rgb * (inVertexColor.a * dayLight.rgb + 
+	color.rgb = inVertexColor.rgb * (inVertexColor.a * dayLight.rgb +
 		nightRatio * artificialLight.rgb) * 2.0;
 	color.a = 1.0;