Fix a DrawElements bug in the Metal backend.

The indexOffset of the draw was not being used. It must be
included in the indexBufferOffset.
Renamed indexBufferOffset -> indexBufferBaseOffset.
Add a DrawElements test which exercises zero and non-zero index offsets.

src/backend/metal/CommandBufferMTL.mm

@@ -167,7 +167,7 @@ namespace backend { namespace metal {
         ComputePipeline* lastComputePipeline = nullptr;
         RenderPipeline* lastRenderPipeline = nullptr;
         id<MTLBuffer> indexBuffer = nil;
-        uint32_t indexBufferOffset = 0;
+        uint32_t indexBufferBaseOffset = 0;
 
         CurrentEncoders encoders;
         encoders.device = mDevice;
@@ -304,6 +304,7 @@ namespace backend { namespace metal {
 
                 case Command::DrawElements: {
                     DrawElementsCmd* draw = mCommands.NextCommand<DrawElementsCmd>();
+                    size_t formatSize = IndexFormatSize(lastRenderPipeline->GetIndexFormat());
 
                     ASSERT(encoders.render);
                     [encoders.render
@@ -311,7 +312,7 @@ namespace backend { namespace metal {
                                    indexCount:draw->indexCount
                                     indexType:lastRenderPipeline->GetMTLIndexType()
                                   indexBuffer:indexBuffer
-                            indexBufferOffset:indexBufferOffset
+                            indexBufferOffset:indexBufferBaseOffset + draw->firstIndex * formatSize
                                 instanceCount:draw->instanceCount
                                    baseVertex:0
                                  baseInstance:draw->firstInstance];
@@ -526,7 +527,7 @@ namespace backend { namespace metal {
                     SetIndexBufferCmd* cmd = mCommands.NextCommand<SetIndexBufferCmd>();
                     auto b = ToBackend(cmd->buffer.Get());
                     indexBuffer = b->GetMTLBuffer();
-                    indexBufferOffset = cmd->offset;
+                    indexBufferBaseOffset = cmd->offset;
                 } break;
 
                 case Command::SetVertexBuffers: {

src/backend/opengl/CommandBufferGL.cpp

@@ -243,7 +243,7 @@ namespace backend { namespace opengl {
         PipelineBase* lastPipeline = nullptr;
         PipelineGL* lastGLPipeline = nullptr;
         RenderPipeline* lastRenderPipeline = nullptr;
-        uint32_t indexBufferOffset = 0;
+        uint32_t indexBufferBaseOffset = 0;
 
         PersistentPipelineState persistentPipelineState;
         persistentPipelineState.SetDefaultState();
@@ -505,7 +505,7 @@ namespace backend { namespace opengl {
                             lastRenderPipeline->GetGLPrimitiveTopology(), draw->indexCount,
                             formatType,
                             reinterpret_cast<void*>(draw->firstIndex * formatSize +
-                                                    indexBufferOffset),
+                                                    indexBufferBaseOffset),
                             draw->instanceCount, draw->firstInstance);
                     } else {
                         // This branch is only needed on OpenGL < 4.2
@@ -513,7 +513,7 @@ namespace backend { namespace opengl {
                             lastRenderPipeline->GetGLPrimitiveTopology(), draw->indexCount,
                             formatType,
                             reinterpret_cast<void*>(draw->firstIndex * formatSize +
-                                                    indexBufferOffset),
+                                                    indexBufferBaseOffset),
                             draw->instanceCount);
                     }
                 } break;
@@ -635,7 +635,7 @@ namespace backend { namespace opengl {
 
                 case Command::SetIndexBuffer: {
                     SetIndexBufferCmd* cmd = mCommands.NextCommand<SetIndexBufferCmd>();
-                    indexBufferOffset = cmd->offset;
+                    indexBufferBaseOffset = cmd->offset;
                     inputBuffers.OnSetIndexBuffer(cmd->buffer.Get());
                 } break;
 

src/tests/CMakeLists.txt

@@ -75,6 +75,7 @@ add_executable(nxt_end2end_tests
     ${END2END_TESTS_DIR}/BufferTests.cpp
     ${END2END_TESTS_DIR}/BlendStateTests.cpp
     ${END2END_TESTS_DIR}/CopyTests.cpp
+    ${END2END_TESTS_DIR}/DrawElementsTests.cpp
     ${END2END_TESTS_DIR}/DepthStencilStateTests.cpp
     ${END2END_TESTS_DIR}/IndexFormatTests.cpp
     ${END2END_TESTS_DIR}/InputStateTests.cpp

src/tests/end2end/DrawElementsTests.cpp

@@ -0,0 +1,137 @@
+// Copyright 2018 The NXT Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include "tests/NXTTest.h"
+
+#include "utils/NXTHelpers.h"
+
+constexpr uint32_t kRTSize = 4;
+
+class DrawElementsTest : public NXTTest {
+    protected:
+        void SetUp() override {
+            NXTTest::SetUp();
+
+            renderpass = device.CreateRenderPassBuilder()
+                .SetAttachmentCount(1)
+                .AttachmentSetFormat(0, nxt::TextureFormat::R8G8B8A8Unorm)
+                .AttachmentSetColorLoadOp(0, nxt::LoadOp::Clear)
+                .SetSubpassCount(1)
+                .SubpassSetColorAttachment(0, 0, 0)
+                .GetResult();
+
+            renderTarget = device.CreateTextureBuilder()
+                .SetDimension(nxt::TextureDimension::e2D)
+                .SetExtent(kRTSize, kRTSize, 1)
+                .SetFormat(nxt::TextureFormat::R8G8B8A8Unorm)
+                .SetMipLevels(1)
+                .SetAllowedUsage(nxt::TextureUsageBit::OutputAttachment | nxt::TextureUsageBit::TransferSrc)
+                .SetInitialUsage(nxt::TextureUsageBit::OutputAttachment)
+                .GetResult();
+
+            renderTargetView = renderTarget.CreateTextureViewBuilder().GetResult();
+
+            framebuffer = device.CreateFramebufferBuilder()
+                .SetRenderPass(renderpass)
+                .SetAttachment(0, renderTargetView)
+                .SetDimensions(kRTSize, kRTSize)
+                .GetResult();
+
+            nxt::InputState inputState = device.CreateInputStateBuilder()
+                .SetInput(0, 4 * sizeof(float), nxt::InputStepMode::Vertex)
+                .SetAttribute(0, 0, nxt::VertexFormat::FloatR32G32B32A32, 0)
+                .GetResult();
+
+            nxt::ShaderModule vsModule = utils::CreateShaderModule(device, nxt::ShaderStage::Vertex, R"(
+                #version 450
+                layout(location = 0) in vec4 pos;
+                void main() {
+                    gl_Position = pos;
+                })"
+            );
+
+            nxt::ShaderModule fsModule = utils::CreateShaderModule(device, nxt::ShaderStage::Fragment, R"(
+                #version 450
+                layout(location = 0) out vec4 fragColor;
+                void main() {
+                    fragColor = vec4(0.0, 1.0, 0.0, 1.0);
+                })"
+            );
+
+            pipeline = device.CreateRenderPipelineBuilder()
+                .SetSubpass(renderpass, 0)
+                .SetPrimitiveTopology(nxt::PrimitiveTopology::TriangleStrip)
+                .SetStage(nxt::ShaderStage::Vertex, vsModule, "main")
+                .SetStage(nxt::ShaderStage::Fragment, fsModule, "main")
+                .SetIndexFormat(nxt::IndexFormat::Uint32)
+                .SetInputState(inputState)
+                .GetResult();
+
+            vertexBuffer = utils::CreateFrozenBufferFromData<float>(device, nxt::BufferUsageBit::Vertex, {
+                -1.0f, -1.0f, 0.0f, 1.0f,
+                 1.0f,  1.0f, 0.0f, 1.0f,
+                -1.0f,  1.0f, 0.0f, 1.0f,
+                 1.0f, -1.0f, 0.0f, 1.0f
+            });
+            indexBuffer = utils::CreateFrozenBufferFromData<uint32_t>(device, nxt::BufferUsageBit::Index, {
+                0, 1, 2, 0, 3, 1
+            });
+        }
+
+        nxt::RenderPass renderpass;
+        nxt::Texture renderTarget;
+        nxt::TextureView renderTargetView;
+        nxt::Framebuffer framebuffer;
+        nxt::RenderPipeline pipeline;
+        nxt::Buffer vertexBuffer;
+        nxt::Buffer indexBuffer;
+
+        void Test(uint32_t indexCount, uint32_t instanceCount, uint32_t firstIndex,
+                  uint32_t firstInstance, RGBA8 bottomLeftExpected, RGBA8 topRightExpected) {
+            uint32_t zeroOffset = 0;
+            nxt::CommandBuffer commands = device.CreateCommandBufferBuilder()
+                .BeginRenderPass(renderpass, framebuffer)
+                .BeginRenderSubpass()
+                    .SetRenderPipeline(pipeline)
+                    .SetVertexBuffers(0, 1, &vertexBuffer, &zeroOffset)
+                    .SetIndexBuffer(indexBuffer, 0)
+                    .DrawElements(indexCount, instanceCount, firstIndex, firstInstance)
+                .EndRenderSubpass()
+                .EndRenderPass()
+                .GetResult();
+
+            queue.Submit(1, &commands);
+
+            EXPECT_PIXEL_RGBA8_EQ(bottomLeftExpected, renderTarget, 1, 3);
+            EXPECT_PIXEL_RGBA8_EQ(topRightExpected, renderTarget, 3, 1);
+        }
+};
+
+// The most basic DrawElements triangle draw.
+TEST_P(DrawElementsTest, Uint32) {
+
+    RGBA8 filled(0, 255, 0, 255);
+    RGBA8 notFilled(0, 0, 0, 0);
+
+    // Test a draw with no indices.
+    Test(0, 0, 0, 0, notFilled, notFilled);
+    // Test a draw with only the first 3 indices (bottom left triangle)
+    Test(3, 1, 0, 0, filled, notFilled);
+    // Test a draw with only the last 3 indices (top right triangle)
+    Test(3, 1, 3, 0, notFilled, filled);
+    // Test a draw with all 6 indices (both triangles).
+    Test(6, 1, 0, 0, filled, filled);
+}
+
+NXT_INSTANTIATE_TEST(DrawElementsTest, MetalBackend, OpenGLBackend, D3D12Backend, VulkanBackend)