Fix undefined memory access in getCoveringRanges() (#9227)

* Add simple unit tests for SymbolSizeBinder

* Fix bug in symbol size uniform value calculation

For camera functions we were setting the zoom levels in "covering ranges" to
`[(zoom stop <= tile zoom), (zoom stop >= 1 + tile zoom)]`, but then evaluating
the function at `[tile_zoom, tile_zoom + 1]`.

* Check for it != end() before accessing it->first

1 files changed, 61 insertions, 0 deletions

diff --git a/test/programs/symbol_program.test.cpp b/test/programs/symbol_program.test.cpp
new file mode 100644
index 0000000000..ef1e71c269
--- /dev/null
+++ b/test/programs/symbol_program.test.cpp
@@ -0,0 +1,61 @@
+#include <mbgl/test/util.hpp>
+
+#include <mbgl/programs/symbol_program.hpp>
+
+using namespace mbgl;
+
+TEST(SymbolProgram, SymbolSizeBinder) {
+    auto binder = SymbolSizeBinder::create(5.0f, 12.0f, 0.0f);
+    auto uniformValues = binder->uniformValues(5.5f);
+    EXPECT_EQ(uniformValues.get<uniforms::u_is_size_zoom_constant>().t, true);
+    EXPECT_EQ(uniformValues.get<uniforms::u_is_size_feature_constant>().t, true);
+    EXPECT_EQ(uniformValues.get<uniforms::u_size>().t, 12.0f);
+    EXPECT_EQ(uniformValues.get<uniforms::u_layout_size>().t, 12.0f);
+
+    binder = SymbolSizeBinder::create(1.0f, style::CameraFunction<float>(style::ExponentialStops<float>({
+        {0.0f, 8.0f},
+        {10.0f, 18.0f}
+    }, 1.0f)), 0.0f);
+    uniformValues = binder->uniformValues(1.5f);
+    EXPECT_EQ(uniformValues.get<uniforms::u_is_size_zoom_constant>().t, false);
+    EXPECT_EQ(uniformValues.get<uniforms::u_is_size_feature_constant>().t, true);
+    EXPECT_EQ(uniformValues.get<uniforms::u_size>().t, 9.5f);
+    EXPECT_EQ(uniformValues.get<uniforms::u_layout_size>().t, 10.0f);
+    
+    binder = SymbolSizeBinder::create(0.0f, style::CameraFunction<float>(style::ExponentialStops<float>({
+        {1.0f, 8.0f},
+        {11.0f, 18.0f}
+    }, 1.0f)), 0.0f);
+    uniformValues = binder->uniformValues(0.5f);
+    EXPECT_EQ(uniformValues.get<uniforms::u_is_size_zoom_constant>().t, false);
+    EXPECT_EQ(uniformValues.get<uniforms::u_is_size_feature_constant>().t, true);
+    EXPECT_EQ(uniformValues.get<uniforms::u_size>().t, 8.0f);
+    EXPECT_EQ(uniformValues.get<uniforms::u_layout_size>().t, 8.0f);
+    
+    binder = SymbolSizeBinder::create(12.0f, style::CameraFunction<float>(style::ExponentialStops<float>({
+        {1.0f, 8.0f},
+        {11.0f, 18.0f}
+    }, 1.0f)), 0.0f);
+    uniformValues = binder->uniformValues(12.5f);
+    EXPECT_EQ(uniformValues.get<uniforms::u_is_size_zoom_constant>().t, false);
+    EXPECT_EQ(uniformValues.get<uniforms::u_is_size_feature_constant>().t, true);
+    EXPECT_EQ(uniformValues.get<uniforms::u_size>().t, 18.0f);
+    EXPECT_EQ(uniformValues.get<uniforms::u_layout_size>().t, 18.0f);
+    
+    binder = SymbolSizeBinder::create(0.0f, style::SourceFunction<float>("x", style::ExponentialStops<float>({
+        {1.0f, 8.0f},
+        {11.0f, 18.0f}
+    }, 1.0f)), 0.0f);
+    uniformValues = binder->uniformValues(12.5f);
+    EXPECT_EQ(uniformValues.get<uniforms::u_is_size_zoom_constant>().t, true);
+    EXPECT_EQ(uniformValues.get<uniforms::u_is_size_feature_constant>().t, false);
+
+    binder = SymbolSizeBinder::create(5.0f, style::CompositeFunction<float>("x", style::CompositeExponentialStops<float>({
+        {1.0f, {{0.0f, 8.0f}, {100.0f, 18.0f}}},
+        {11.0f, {{0.0f, 12.0f}, {100.0f, 24.9f}}}
+    }, 1.0f)), 0.0f);
+    uniformValues = binder->uniformValues(5.5f);
+    EXPECT_EQ(uniformValues.get<uniforms::u_is_size_zoom_constant>().t, false);
+    EXPECT_EQ(uniformValues.get<uniforms::u_is_size_feature_constant>().t, false);
+    EXPECT_EQ(uniformValues.get<uniforms::u_size_t>().t, 0.45f);
+}