Pack preloaded framework assets in a texture atlas

When the Android runtime starts, the system preloads a series of assets
in the Zygote process. These assets are shared across all processes.
Unfortunately, each one of these assets is later uploaded in its own
OpenGL texture, once per process. This wastes memory and generates
unnecessary OpenGL state changes.

This CL introduces an asset server that provides an atlas to all processes.

Note: bitmaps used by skia shaders are *not* sampled from the atlas.
It's an uncommon use case and would require extra texture transforms
in the GL shaders.

WHAT IS THE ASSETS ATLAS

The "assets atlas" is a single, shareable graphic buffer that contains
all the system's preloaded bitmap drawables (this includes 9-patches.)
The atlas is made of two distinct objects: the graphic buffer that
contains the actual pixels and the map which indicates where each
preloaded bitmap can be found in the atlas (essentially a pair of
x and y coordinates.)

HOW IS THE ASSETS ATLAS GENERATED

Because we need to support a wide variety of devices and because it
is easy to change the list of preloaded drawables, the atlas is
generated at runtime, during the startup phase of the system process.

There are several steps that lead to the atlas generation:

1. If the device is booting for the first time, or if the device was
updated, we need to find the best atlas configuration. To do so,
the atlas service tries a number of width, height and algorithm
variations that allows us to pack as many assets as possible while
using as little memory as possible. Once a best configuration is found,
it gets written to disk in /data/system/framework_atlas

2. Given a best configuration (algorithm variant, dimensions and
number of bitmaps that can be packed in the atlas), the atlas service
packs all the preloaded bitmaps into a single graphic buffer object.

3. The packing is done using Skia in a temporary native bitmap. The
Skia bitmap is then copied into the graphic buffer using OpenGL ES
to benefit from texture swizzling.

HOW PROCESSES USE THE ATLAS

Whenever a process' hardware renderer initializes its EGL context,
it queries the atlas service for the graphic buffer and the map.

It is important to remember that both the context and the map will
be valid for the lifetime of the hardware renderer (if the system
process goes down, all apps get killed as well.)

Every time the hardware renderer needs to render a bitmap, it first
checks whether the bitmap can be found in the assets atlas. When
the bitmap is part of the atlas, texture coordinates are remapped
appropriately before rendering.

Change-Id: I8eaecf53e7f6a33d90da3d0047c5ceec89ea3af0

1 files changed, 24 insertions, 11 deletions

diff --git a/libs/hwui/Program.cpp b/libs/hwui/Program.cpp
index 14a23765b301..c127d684be32 100644
--- a/libs/hwui/Program.cpp
+++ b/libs/hwui/Program.cpp
@@ -15,6 +15,9 @@
  */
 
 #define LOG_TAG "OpenGLRenderer"
+#define ATRACE_TAG ATRACE_TAG_VIEW
+
+#include <utils/Trace.h>
 
 #include "Program.h"
 
@@ -25,7 +28,6 @@ namespace uirenderer {
 // Base program
 ///////////////////////////////////////////////////////////////////////////////
 
-// TODO: Program instance should be created from a factory method
 Program::Program(const ProgramDescription& description, const char* vertex, const char* fragment) {
     mInitialized = false;
     mHasColorUniform = false;
@@ -50,7 +52,9 @@ Program::Program(const ProgramDescription& description, const char* vertex, cons
                 texCoords = -1;
             }
 
+            ATRACE_BEGIN("linkProgram");
             glLinkProgram(mProgramId);
+            ATRACE_END();
 
             GLint status;
             glGetProgramiv(mProgramId, GL_LINK_STATUS, &status);
@@ -87,6 +91,9 @@ Program::Program(const ProgramDescription& description, const char* vertex, cons
 
 Program::~Program() {
     if (mInitialized) {
+        // This would ideally happen after linking the program
+        // but Tegra drivers, especially when perfhud is enabled,
+        // sometimes crash if we do so
         glDetachShader(mProgramId, mVertexShader);
         glDetachShader(mProgramId, mFragmentShader);
 
@@ -132,6 +139,8 @@ int Program::getUniform(const char* name) {
 }
 
 GLuint Program::buildShader(const char* source, GLenum type) {
+    ATRACE_CALL();
+
     GLuint shader = glCreateShader(type);
     glShaderSource(shader, 1, &source, 0);
     glCompileShader(shader);
@@ -153,20 +162,24 @@ GLuint Program::buildShader(const char* source, GLenum type) {
 
 void Program::set(const mat4& projectionMatrix, const mat4& modelViewMatrix,
         const mat4& transformMatrix, bool offset) {
-    mat4 p(projectionMatrix);
-    if (offset) {
-        // offset screenspace xy by an amount that compensates for typical precision
-        // issues in GPU hardware that tends to paint hor/vert lines in pixels shifted
-        // up and to the left.
-        // This offset value is based on an assumption that some hardware may use as
-        // little as 12.4 precision, so we offset by slightly more than 1/16.
-        p.translate(.065, .065, 0);
+    if (projectionMatrix != mProjection) {
+        if (CC_LIKELY(!offset)) {
+            glUniformMatrix4fv(projection, 1, GL_FALSE, &projectionMatrix.data[0]);
+        } else {
+            mat4 p(projectionMatrix);
+            // offset screenspace xy by an amount that compensates for typical precision
+            // issues in GPU hardware that tends to paint hor/vert lines in pixels shifted
+            // up and to the left.
+            // This offset value is based on an assumption that some hardware may use as
+            // little as 12.4 precision, so we offset by slightly more than 1/16.
+            p.translate(.065, .065, 0);
+            glUniformMatrix4fv(projection, 1, GL_FALSE, &p.data[0]);
+        }
+        mProjection = projectionMatrix;
     }
 
     mat4 t(transformMatrix);
     t.multiply(modelViewMatrix);
-
-    glUniformMatrix4fv(projection, 1, GL_FALSE, &p.data[0]);
     glUniformMatrix4fv(transform, 1, GL_FALSE, &t.data[0]);
 }