Low-Level Test Results: Alpha Blending
The Alpha Blending test begins by drawing 50 squares on each other. Then, it measures the frame rate. If the FPS result is above 25, it draws more squares. If it's below 20 FPS, it removes squares. The test changes the number of drawn elements in each frame until the scene runs steadily between 20 and 25 FPS.
As you'll see in the chart below, the test's score is reported in megabytes per second, which is the representation of how many total layers (of different sizes) the GPU was able to blend over each other, measuring the processor's alpha-blended overdraw capability. In a time of hardware-accelerated UIs, extensive particle systems, and render-to-texture effects, this is an important number.
What subsystems in the graphics pipeline are involved in this test? That varies, depending on the architecture. But memory operations, rasterization, and fill play significant roles.
This test renders semi-transparent quads using high-resolution, uncompressed textures to strain the GPU.
As we'll discover, there's not a ton of difference overall between on- and off-screen testing with this metric, telling us that resolution isn't our bottleneck. Google's Nexus 5 wins, demonstrating a 37% advantage over the second-place iPhone 5s, despite pushing significantly more pixels. The 2013 Google Nexus 7 takes third place, around 7% slower than iPhone 5s.
Meizu's MX3 and Oppo's N1 pretty much share the fourth and fifth spot. The MX3’s PowerVR SGX544MP3 GPU core might be dated, but its TBDR architecture seems to be shining through, at only 18% slower than the iPhone 5s at native resolution. The Oppo N1, on the other hand, seems to again be suffering for its Android 4.2-based ColorOS; those overlays always come at a cost to performance.
The Galaxy Note 10.1” 2014 Edition is really straining under the combined weight of its QHD pixel count and TouchWiz UI. But EVGA's Note 7 disappoints most. It has a reasonably low-res screen and almost no UI customization, so we can only point to Tegra 4 and its modest memory subsystem.
A bit of reordering does take place here. Google's Nexus 5 and Apple's iPhone 5s maintain their first and second places, respectively. And the Nexus 7 still sits behind the iPhone 5s.
Oppo N1's moves up the ladder one place, seemingly less hampered by whatever overlays ColorOS is hooking in place. Still, it does seem to suffer a little against the supposedly less powerful Nexus 7, probably due to Google’s native Android 4.4.2, and in particular, better HWCompose support.
The Meizu MX3 moves down a spot in response to the Oppo N1 breaking free of its overlays, though the performance of that device doesn't really change.
Similarly, the Tegra Note 7 moves up a spot, while returning a score in the same territory.
We see another Exynos 5 Octa-based device at the bottom of the pile, though the Galaxy Note 10.1” should be without the twin strains of TouchWiz and its own imposing native pixel count. We'd be inclined to point at its Mali-T628MP6 graphics engine.