Don't skip draw calls on zero-sized viewports.

src/libGLESv2/Context.cpp

@@ -1325,7 +1325,7 @@ bool Context::getIndexedQueryParameterInfo(GLenum target, GLenum *type, unsigned
 
 // Applies the render target surface, depth stencil surface, viewport rectangle and
 // scissor rectangle to the renderer
-bool Context::applyRenderTarget(GLenum drawMode, bool ignoreViewport)
+void Context::applyRenderTarget(GLenum drawMode, bool ignoreViewport)
 {
     Framebuffer *framebufferObject = mState.getDrawFramebuffer();
     ASSERT(framebufferObject && framebufferObject->completeness() == GL_FRAMEBUFFER_COMPLETE);
@@ -1334,15 +1334,10 @@ bool Context::applyRenderTarget(GLenum drawMode, bool ignoreViewport)
 
     float nearZ, farZ;
     mState.getDepthRange(&nearZ, &farZ);
-    if (!mRenderer->setViewport(mState.getViewport(), nearZ, farZ, drawMode, mState.getRasterizerState().frontFace,
-                                ignoreViewport))
-    {
-        return false;
-    }
+    mRenderer->setViewport(mState.getViewport(), nearZ, farZ, drawMode, mState.getRasterizerState().frontFace,
+                           ignoreViewport);
 
     mRenderer->setScissorRectangle(mState.getScissor(), mState.isScissorTestEnabled());
-
-    return true;
 }
 
 // Applies the fixed-function state (culling, depth test, alpha blending, stenciling, etc) to the Direct3D 9 device
@@ -1561,10 +1556,7 @@ Error Context::clear(GLbitfield mask)
 
     ClearParameters clearParams = mState.getClearParameters(mask);
 
-    if (!applyRenderTarget(GL_TRIANGLES, true))   // Clips the clear to the scissor rectangle but not the viewport
-    {
-        return Error(GL_NO_ERROR);
-    }
+    applyRenderTarget(GL_TRIANGLES, true);   // Clips the clear to the scissor rectangle but not the viewport
 
     return mRenderer->clear(clearParams, mState.getDrawFramebuffer());
 }
@@ -1595,10 +1587,7 @@ Error Context::clearBufferfv(GLenum buffer, int drawbuffer, const float *values)
         clearParams.depthClearValue = values[0];
     }
 
-    if (!applyRenderTarget(GL_TRIANGLES, true))   // Clips the clear to the scissor rectangle but not the viewport
-    {
-        return Error(GL_NO_ERROR);
-    }
+    applyRenderTarget(GL_TRIANGLES, true);   // Clips the clear to the scissor rectangle but not the viewport
 
     return mRenderer->clear(clearParams, mState.getDrawFramebuffer());
 }
@@ -1619,10 +1608,7 @@ Error Context::clearBufferuiv(GLenum buffer, int drawbuffer, const unsigned int
     clearParams.colorUIClearValue = ColorUI(values[0], values[1], values[2], values[3]);
     clearParams.colorClearType = GL_UNSIGNED_INT;
 
-    if (!applyRenderTarget(GL_TRIANGLES, true))   // Clips the clear to the scissor rectangle but not the viewport
-    {
-        return Error(GL_NO_ERROR);
-    }
+    applyRenderTarget(GL_TRIANGLES, true);   // Clips the clear to the scissor rectangle but not the viewport
 
     return mRenderer->clear(clearParams, mState.getDrawFramebuffer());
 }
@@ -1653,10 +1639,7 @@ Error Context::clearBufferiv(GLenum buffer, int drawbuffer, const int *values)
         clearParams.stencilClearValue = values[1];
     }
 
-    if (!applyRenderTarget(GL_TRIANGLES, true))   // Clips the clear to the scissor rectangle but not the viewport
-    {
-        return Error(GL_NO_ERROR);
-    }
+    applyRenderTarget(GL_TRIANGLES, true);   // Clips the clear to the scissor rectangle but not the viewport
 
     return mRenderer->clear(clearParams, mState.getDrawFramebuffer());
 }
@@ -1675,10 +1658,7 @@ Error Context::clearBufferfi(GLenum buffer, int drawbuffer, float depth, int ste
     clearParams.clearStencil = true;
     clearParams.stencilClearValue = stencil;
 
-    if (!applyRenderTarget(GL_TRIANGLES, true))   // Clips the clear to the scissor rectangle but not the viewport
-    {
-        return Error(GL_NO_ERROR);
-    }
+    applyRenderTarget(GL_TRIANGLES, true);   // Clips the clear to the scissor rectangle but not the viewport
 
     return mRenderer->clear(clearParams, mState.getDrawFramebuffer());
 }
@@ -1721,11 +1701,7 @@ void Context::drawArrays(GLenum mode, GLint first, GLsizei count, GLsizei instan
         return;
     }
 
-    if (!applyRenderTarget(mode, false))
-    {
-        return;
-    }
-
+    applyRenderTarget(mode, false);
     applyState(mode);
 
     GLenum err = mRenderer->applyVertexBuffer(programBinary, mState.getVertexArray()->getVertexAttributes(), mState.getVertexAttribCurrentValues(), first, count, instances);
@@ -1787,11 +1763,7 @@ void Context::drawElements(GLenum mode, GLsizei count, GLenum type,
         return;
     }
 
-    if (!applyRenderTarget(mode, false))
-    {
-        return;
-    }
-
+    applyRenderTarget(mode, false);
     applyState(mode);
 
     VertexArray *vao = mState.getVertexArray();

src/libGLESv2/Context.h

@@ -234,7 +234,7 @@ class Context
     // TODO: std::array may become unavailable using older versions of GCC
     typedef std::array<unsigned int, IMPLEMENTATION_MAX_FRAMEBUFFER_ATTACHMENTS> FramebufferTextureSerialArray;
 
-    bool applyRenderTarget(GLenum drawMode, bool ignoreViewport);
+    void applyRenderTarget(GLenum drawMode, bool ignoreViewport);
     void applyState(GLenum drawMode);
     void applyShaders(ProgramBinary *programBinary, bool transformFeedbackActive);
     void applyTextures(SamplerType shaderType, Texture *textures[], TextureType *textureTypes, SamplerState *samplers,

src/libGLESv2/renderer/Renderer.h

@@ -125,7 +125,7 @@ class Renderer
                                       int stencilBackRef, bool frontFaceCCW) = 0;
 
     virtual void setScissorRectangle(const gl::Rectangle &scissor, bool enabled) = 0;
-    virtual bool setViewport(const gl::Rectangle &viewport, float zNear, float zFar, GLenum drawMode, GLenum frontFace,
+    virtual void setViewport(const gl::Rectangle &viewport, float zNear, float zFar, GLenum drawMode, GLenum frontFace,
                              bool ignoreViewport) = 0;
 
     virtual bool applyRenderTarget(gl::Framebuffer *frameBuffer) = 0;

src/libGLESv2/renderer/d3d/d3d11/Renderer11.cpp

@@ -697,7 +697,7 @@ void Renderer11::setScissorRectangle(const gl::Rectangle &scissor, bool enabled)
     mForceSetScissor = false;
 }
 
-bool Renderer11::setViewport(const gl::Rectangle &viewport, float zNear, float zFar, GLenum drawMode, GLenum frontFace, 
+void Renderer11::setViewport(const gl::Rectangle &viewport, float zNear, float zFar, GLenum drawMode, GLenum frontFace,
                              bool ignoreViewport)
 {
     gl::Rectangle actualViewport = viewport;
@@ -724,11 +724,6 @@ bool Renderer11::setViewport(const gl::Rectangle &viewport, float zNear, float z
     dxViewport.MinDepth = actualZNear;
     dxViewport.MaxDepth = actualZFar;
 
-    if (dxViewport.Width <= 0 || dxViewport.Height <= 0)
-    {
-        return false;   // Nothing to render
-    }
-
     bool viewportChanged = mForceSetViewport || memcmp(&actualViewport, &mCurViewport, sizeof(gl::Rectangle)) != 0 ||
                            actualZNear != mCurNear || actualZFar != mCurFar;
 
@@ -758,7 +753,6 @@ bool Renderer11::setViewport(const gl::Rectangle &viewport, float zNear, float z
     }
 
     mForceSetViewport = false;
-    return true;
 }
 
 bool Renderer11::applyPrimitiveType(GLenum mode, GLsizei count)

src/libGLESv2/renderer/d3d/d3d11/Renderer11.h

@@ -72,7 +72,7 @@ class Renderer11 : public Renderer
                                       int stencilBackRef, bool frontFaceCCW);
 
     virtual void setScissorRectangle(const gl::Rectangle &scissor, bool enabled);
-    virtual bool setViewport(const gl::Rectangle &viewport, float zNear, float zFar, GLenum drawMode, GLenum frontFace,
+    virtual void setViewport(const gl::Rectangle &viewport, float zNear, float zFar, GLenum drawMode, GLenum frontFace,
                              bool ignoreViewport);
 
     virtual bool applyPrimitiveType(GLenum mode, GLsizei count);

src/libGLESv2/renderer/d3d/d3d9/Renderer9.cpp

@@ -964,7 +964,7 @@ void Renderer9::setScissorRectangle(const gl::Rectangle &scissor, bool enabled)
     mForceSetScissor = false;
 }
 
-bool Renderer9::setViewport(const gl::Rectangle &viewport, float zNear, float zFar, GLenum drawMode, GLenum frontFace,
+void Renderer9::setViewport(const gl::Rectangle &viewport, float zNear, float zFar, GLenum drawMode, GLenum frontFace,
                             bool ignoreViewport)
 {
     gl::Rectangle actualViewport = viewport;
@@ -988,11 +988,6 @@ bool Renderer9::setViewport(const gl::Rectangle &viewport, float zNear, float zF
     dxViewport.MinZ = actualZNear;
     dxViewport.MaxZ = actualZFar;
 
-    if (dxViewport.Width <= 0 || dxViewport.Height <= 0)
-    {
-        return false;   // Nothing to render
-    }
-
     float depthFront = !gl::IsTriangleMode(drawMode) ? 0.0f : (frontFace == GL_CCW ? 1.0f : -1.0f);
 
     bool viewportChanged = mForceSetViewport || memcmp(&actualViewport, &mCurViewport, sizeof(gl::Rectangle)) != 0 ||
@@ -1045,7 +1040,6 @@ bool Renderer9::setViewport(const gl::Rectangle &viewport, float zNear, float zF
     }
 
     mForceSetViewport = false;
-    return true;
 }
 
 bool Renderer9::applyPrimitiveType(GLenum mode, GLsizei count)

src/libGLESv2/renderer/d3d/d3d9/Renderer9.h

@@ -73,7 +73,7 @@ class Renderer9 : public Renderer
                                       int stencilBackRef, bool frontFaceCCW);
 
     virtual void setScissorRectangle(const gl::Rectangle &scissor, bool enabled);
-    virtual bool setViewport(const gl::Rectangle &viewport, float zNear, float zFar, GLenum drawMode, GLenum frontFace,
+    virtual void setViewport(const gl::Rectangle &viewport, float zNear, float zFar, GLenum drawMode, GLenum frontFace,
                              bool ignoreViewport);
 
     virtual bool applyRenderTarget(gl::Framebuffer *frameBuffer);

tests/angle_tests/TransformFeedbackTest.cpp

+#include "ANGLETest.h"
+
+class TransformFeedbackTest : public ANGLETest
+{
+  protected:
+      TransformFeedbackTest()
+    {
+        setWindowWidth(128);
+        setWindowHeight(128);
+        setConfigRedBits(8);
+        setConfigGreenBits(8);
+        setConfigBlueBits(8);
+        setConfigAlphaBits(8);
+        setClientVersion(3);
+    }
+
+    virtual void SetUp()
+    {
+        ANGLETest::SetUp();
+
+        const std::string vertexShaderSource = SHADER_SOURCE
+        (
+            precision highp float;
+            attribute vec4 position;
+
+            void main()
+            {
+                gl_Position = position;
+            }
+        );
+
+        const std::string fragmentShaderSource = SHADER_SOURCE
+        (
+            precision highp float;
+
+            void main()
+            {
+                gl_FragColor = vec4(1.0, 0.0, 0.0, 1.0);
+            }
+        );
+
+        mProgram = CompileProgram(vertexShaderSource, fragmentShaderSource);
+        if (mProgram == 0)
+        {
+            FAIL() << "shader compilation failed.";
+        }
+
+        glGenBuffers(1, &mTransformFeedbackBuffer);
+        mTransformFeedbackBufferSize = 1 << 24; // ~16MB
+        glBindBuffer(GL_TRANSFORM_FEEDBACK_BUFFER, mTransformFeedbackBuffer);
+        glBufferData(GL_TRANSFORM_FEEDBACK_BUFFER, mTransformFeedbackBufferSize, NULL, GL_STATIC_DRAW);
+
+        ASSERT_GL_NO_ERROR();
+    }
+
+    virtual void TearDown()
+    {
+        glDeleteProgram(mProgram);
+        glDeleteBuffers(1, &mTransformFeedbackBuffer);
+        ANGLETest::TearDown();
+    }
+
+    GLuint mProgram;
+
+    size_t mTransformFeedbackBufferSize;
+    GLuint mTransformFeedbackBuffer;
+};
+
+TEST_F(TransformFeedbackTest, ZeroSizedViewport)
+{
+    // Set the program's transform feedback varyings (just gl_Position)
+    const GLchar* transformFeedbackVaryings[] =
+    {
+        "gl_Position"
+    };
+    glTransformFeedbackVaryings(mProgram, ArraySize(transformFeedbackVaryings), transformFeedbackVaryings, GL_INTERLEAVED_ATTRIBS);
+    glLinkProgram(mProgram);
+
+    // Re-link the program
+    GLint linkStatus;
+    glGetProgramiv(mProgram, GL_LINK_STATUS, &linkStatus);
+    ASSERT_NE(linkStatus, 0);
+
+    glUseProgram(mProgram);
+
+    // Bind the buffer for transform feedback output and start transform feedback
+    glBindBufferBase(GL_TRANSFORM_FEEDBACK_BUFFER, 0, mTransformFeedbackBuffer);
+    glBeginTransformFeedback(GL_TRIANGLES);
+
+    // Create a query to check how many primitives were written
+    GLuint primitivesWrittenQuery = 0;
+    glGenQueries(1, &primitivesWrittenQuery);
+    glBeginQuery(GL_TRANSFORM_FEEDBACK_PRIMITIVES_WRITTEN, primitivesWrittenQuery);
+
+    // Set a viewport that would result in no pixels being written to the framebuffer and draw
+    // a quad
+    glViewport(0, 0, 0, 0);
+
+    drawQuad(mProgram, "position", 0.5f);
+
+    // End the query and transform feedkback
+    glEndQuery(GL_TRANSFORM_FEEDBACK_PRIMITIVES_WRITTEN);
+    glEndTransformFeedback();
+
+    // Check how many primitives were written and verify that some were written even if
+    // no pixels were rendered
+    GLuint primitivesWritten = 0;
+    glGetQueryObjectuiv(primitivesWrittenQuery, GL_QUERY_RESULT_EXT, &primitivesWritten);
+    EXPECT_GL_NO_ERROR();
+
+    EXPECT_EQ(primitivesWritten, 2);
+}