1 files changed, 75 insertions, 0 deletions
diff --git a/src/runtime/shaders/distancefieldtext_dropshadow.vert b/src/runtime/shaders/distancefieldtext_dropshadow.vert
new file mode 100644
index 0000000..69fd211
--- /dev/null
+++ b/src/runtime/shaders/distancefieldtext_dropshadow.vert
@@ -0,0 +1,75 @@
+uniform highp mat4 mvp;
+uniform highp mat4 modelView;
+uniform highp float fontScale;
+uniform int textureWidth;
+uniform int textureHeight;
+uniform highp vec2 shadowOffset;
+
+attribute highp vec4 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 highp 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 = highp vec2(1.0 / highp float(textureWidth), 1.0 / highp float(textureHeight));
+
+    sampleCoord = tCoord * textureSizeMultiplier;
+    shadowSampleCoord = (tCoord - shadowOffset) * textureSizeMultiplier;
+    normalizedTextureBounds = highp vec4(textureBounds.xy * textureSizeMultiplier,
+                                         textureBounds.zw * textureSizeMultiplier);
+
+    gl_Position = mvp * vCoord;
+}