Fix crash when viewport Y position is negative

src/OpenGL/libGLESv2/Device.cpp

@@ -817,6 +817,12 @@ namespace es2
 				scissor.y1 = min(scissor.y1, stencilBuffer->getHeight());
 			}
 
+			// Ensure scissor range is positive
+			scissor.x0 = max(scissor.x0, 0);
+			scissor.x1 = max(scissor.x1, 0);
+			scissor.y0 = max(scissor.y0, 0);
+			scissor.y1 = max(scissor.y1, 0);
+
 			setScissor(scissor);
 		}
 

src/Pipeline/SetupRoutine.cpp

@@ -175,14 +175,17 @@ namespace sw
 				yMax = (yMax + 0x0F) >> 4;
 			}
 
-			If(yMin == yMax)
+			yMin = Max(yMin, *Pointer<Int>(data + OFFSET(DrawData,scissorY0)));
+			yMax = Min(yMax, *Pointer<Int>(data + OFFSET(DrawData,scissorY1)));
+
+			// If yMin and yMax are initially negative, the scissor clamping above will typically result
+			// in yMin == 0 and yMax unchanged. We bail as we don't need to rasterize this primitive, and
+			// code below assumes yMin < yMax.
+			If(yMin >= yMax)
 			{
 				Return(false);
 			}
 
-			yMin = Max(yMin, *Pointer<Int>(data + OFFSET(DrawData,scissorY0)));
-			yMax = Min(yMax, *Pointer<Int>(data + OFFSET(DrawData,scissorY1)));
-
 			For(Int q = 0, q < state.multiSample, q++)
 			{
 				Array<Int> Xq(16);

src/Shader/SetupRoutine.cpp

@@ -189,14 +189,17 @@ namespace sw
 				yMax = (yMax + 0x0F) >> 4;
 			}
 
-			If(yMin == yMax)
+			yMin = Max(yMin, *Pointer<Int>(data + OFFSET(DrawData,scissorY0)));
+			yMax = Min(yMax, *Pointer<Int>(data + OFFSET(DrawData,scissorY1)));
+
+			// If yMin and yMax are initially negative, the scissor clamping above will typically result
+			// in yMin == 0 and yMax unchanged. We bail as we don't need to rasterize this primitive, and
+			// code below assumes yMin < yMax.
+			If(yMin >= yMax)
 			{
 				Return(false);
 			}
 
-			yMin = Max(yMin, *Pointer<Int>(data + OFFSET(DrawData,scissorY0)));
-			yMax = Min(yMax, *Pointer<Int>(data + OFFSET(DrawData,scissorY1)));
-
 			For(Int q = 0, q < state.multiSample, q++)
 			{
 				Array<Int> Xq(16);

tests/GLESUnitTests/unittests.cpp

@@ -1174,6 +1174,58 @@ TEST_F(SwiftShaderTest, OutOfMemory)
 	}
 }
 
+TEST_F(SwiftShaderTest, ViewportBounds)
+{
+	auto doRenderWithViewportSettings = [&](GLint x, GLint y, GLsizei w, GLsizei h)
+	{
+		Initialize(3, false);
+
+		std::string vs =
+			"#version 300 es\n"
+			"in vec4 position;\n"
+			"out float unfoldable;\n"
+			"void main()\n"
+			"{\n"
+			"    unfoldable = position.x;\n"
+			"    gl_Position = vec4(position.xy, 0.0, 1.0);\n"
+			"}\n";
+
+		std::string fs =
+			"#version 300 es\n"
+			"precision mediump float;\n"
+			"in float unfoldable;\n"
+			"out vec4 fragColor;\n"
+			"void main()\n"
+			"{\n"
+			"    fragColor = vec4(1.0, 1.0, 1.0, 1.0);\n"
+			"}\n";
+
+		const ProgramHandles ph = createProgram(vs, fs);
+
+		glUseProgram(ph.program);
+
+		glViewport(x, y, w, h);
+
+		drawQuad(ph.program);
+		EXPECT_GLENUM_EQ(GL_NONE, glGetError());
+
+		deleteProgram(ph);
+		Uninitialize();
+	};
+
+	GLsizei w = 100;
+	GLsizei h = 100;
+	GLint minPos = -2000;
+
+	doRenderWithViewportSettings(0, 0, 0, 0);
+	doRenderWithViewportSettings(0, 0, w, h);
+
+	// Negative positions
+	doRenderWithViewportSettings(minPos, 0, w, h);
+	doRenderWithViewportSettings(0, minPos, w, h);
+	doRenderWithViewportSettings(minPos, minPos, w, h);
+}
+
 // Test using TexImage2D to define a rectangle texture
 
 TEST_F(SwiftShaderTest, TextureRectangle_TexImage2D)