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, 78 insertions, 0 deletions

diff --git a/src/Runtime/res/effectlib/distancefieldtext_dropshadow.vert b/src/Runtime/res/effectlib/distancefieldtext_dropshadow.vert
new file mode 100644
index 00000000..f645eb8c
--- /dev/null
+++ b/src/Runtime/res/effectlib/distancefieldtext_dropshadow.vert
@@ -0,0 +1,78 @@
+uniform highp mat4 mvp;
+uniform highp mat4 modelView;
+uniform highp float fontScale;
+uniform int textureWidth;
+uniform int textureHeight;
+uniform highp vec2 shadowOffset;
+
+attribute highp vec3 vCoord;
+attribute highp vec2 tCoord;
+attribute highp vec4 textureBounds;
+
+varying highp vec2 sampleCoord;
+varying highp vec2 shadowSampleCoord;
+varying highp vec2 alphas;
+varying highp vec4 normalizedTextureBounds;
+
+highp float thresholdFunc(highp float scale)
+{
+    highp float base = 0.5;
+    highp float baseDev = 0.065;
+    highp float devScaleMin = 0.15;
+    highp float devScaleMax = 0.3;
+    return base - ((clamp(scale, devScaleMin, devScaleMax) - devScaleMin)
+                   / (devScaleMax - devScaleMin) * -baseDev + baseDev);
+}
+
+highp float spreadFunc(highp float scale)
+{
+    return 0.06 / scale;
+}
+
+highp vec2 alphaRange(highp float scale)
+{
+    highp float base = thresholdFunc(scale);
+    highp float range = spreadFunc(scale);
+    highp float alphaMin = max(0.0, base - range);
+    highp float alphaMax = min(base + range, 1.0);
+    return vec2(alphaMin, alphaMax);
+}
+
+highp float determinantOfSubmatrix(highp mat4 m, int col0, int col1, int row0, int row1)
+{
+    return m[col0][row0] * m[col1][row1] - m[col0][row1] * m[col1][row0];
+}
+
+highp float determinantOfSubmatrix(highp mat4 m, int col0, int col1, int col2,
+                                   int row0, int row1, int row2)
+{
+    highp float det = m[col0][row0] * determinantOfSubmatrix(m, col1, col2, row1, row2);
+    det            -= m[col1][row0] * determinantOfSubmatrix(m, col0, col2, row1, row2);
+    det            += m[col2][row0] * determinantOfSubmatrix(m, col0, col1, row1, row2);
+    return det;
+}
+
+highp float determinant(highp mat4 m)
+{
+    highp float det = m[0][0] * determinantOfSubmatrix(m, 1, 2, 3, 1, 2, 3);
+    det            -= m[1][0] * determinantOfSubmatrix(m, 0, 2, 3, 1, 2, 3);
+    det            += m[2][0] * determinantOfSubmatrix(m, 0, 1, 3, 1, 2, 3);
+    det            -= m[3][0] * determinantOfSubmatrix(m, 0, 1, 2, 1, 2, 3);
+    return det;
+}
+
+void main()
+{
+    highp float scale = fontScale * sqrt(abs(determinant(modelView)));
+    alphas = alphaRange(scale);
+
+    highp vec2 textureSizeMultiplier = vec2(1.0 / highp float(textureWidth),
+                                            1.0 / float(textureHeight));
+
+    sampleCoord = tCoord * textureSizeMultiplier;
+    shadowSampleCoord = (tCoord - shadowOffset) * textureSizeMultiplier;
+    normalizedTextureBounds = highp vec4(textureBounds.xy * textureSizeMultiplier,
+                                         textureBounds.zw * textureSizeMultiplier);
+
+    gl_Position = mvp * vec4(vCoord, 1.0);
+}