Add distance field rendering to OpenGL runtime

The old text rendering remains in the background and is used to render
clipped text, since that feature is not yet implemented for distance
field fonts. Building the runtime with Qt version older than 5.12.2 also
causes a fallback to the old text rendering.

Depth pass rendering also needs to be redone in the future to avoid
another full render pass.

Task-number: QT3DS-3210
Change-Id: Ib7666c437d23ae25e1872682f010df3721476a14
Reviewed-by: Tomi Korpipää <tomi.korpipaa@qt.io>

1 files changed, 14 insertions, 0 deletions

diff --git a/src/Runtime/res/effectlib/distancefieldtext_core.frag b/src/Runtime/res/effectlib/distancefieldtext_core.frag
new file mode 100644
index 00000000..0f848bc1
--- /dev/null
+++ b/src/Runtime/res/effectlib/distancefieldtext_core.frag
@@ -0,0 +1,14 @@
+in vec2 sampleCoord;
+
+out vec4 fragColor;
+
+uniform sampler2D _qt_texture;
+uniform vec4 color;
+
+in vec2 alphas;
+
+void main()
+{
+    fragColor = color * smoothstep(alphas.x, alphas.y,
+                                   texture(_qt_texture, sampleCoord).r);
+}