1 Pixelflinger
1.1 Pixelflinger 简介
Pixelflinger是Android系统中为OpenGLES引擎提供的一套软件渲染器（renderer）。OpenGLES引擎提供了一系列基础绘图功能。这些功能包括定义各种颜色格式像素位置、画点画线、绘制矩形及三角形、填充纹理等等。由于OpenGLES相当于一个状态机，配置OpenGLEs状态的函数也均由Pixelflinger提供。
Pixelflinger涉及到的代码路径：
system/core/libpixelflinger
system/core/include/libpixelflinger
system/core/include/private/pixelflinger
1.2 Pixelflinger生成的库
libpixelflinger_armv6.a
libpixelflinger_static.a
libpixelflinger.so
1.3 Pixelflinger两大数据结构
1.3.1 context_t 结构
该结构是Pixelflinger的主结构，里面含有GGLContext接口结构和state、format等属性。
system/core/include/private/pixelflinger/ggl_context.h
struct context_t {
GGLContext procs;
state_t state;
shade_t shade;
iterators_t iterators;
generated_vars_t generated_vars __attribute__((aligned(32)));
uint8_t ditherMatrix[GGL_DITHER_SIZE] __attribute__((aligned(32)));
uint32_t packed;
uint32_t packed8888;
const GGLFormat* formats;
uint32_t dirty;
texture_t* activeTMU;
uint32_t activeTMUIndex;
void (*init_y)(context_t* c, int32_t y);
void (*step_y)(context_t* c);
void (*scanline)(context_t* c);
void (*span)(context_t* c);
void (*rect)(context_t* c, size_t yc);
void* base;
Assembly* scanline_as;
GGLenum error;
};
1.3.2 GGLContext 结构
Pixelflinger对外是用GGLContext结构提供接口引用的，如下是GGLContext结构形式。
system/core/include/pixelflinger/pixelflinger.h
typedef struct {
// immediate rendering
void (*pointx)(void *con,const GGLcoord* v, GGLcoord r);
void (*linex)(void *con,
const GGLcoord*v0, const GGLcoord* v1, GGLcoord width);
void (*recti)(void* c,GGLint l, GGLint t, GGLint r, GGLint b);
void (*trianglex)(void* c,
GGLcoord const*v0, GGLcoord const* v1, GGLcoord const* v2);
// scissor
void (*scissor)(void* c,GGLint x, GGLint y, GGLsizei width, GGLsizei height);
// Set the textures andcolor buffers
void(*activeTexture)(void* c, GGLuint tmu);
void (*bindTexture)(void*c, const GGLSurface* surface);
void (*colorBuffer)(void*c, const GGLSurface* surface);
void (*readBuffer)(void*c, const GGLSurface* surface);
void (*depthBuffer)(void*c, const GGLSurface* surface);
void(*bindTextureLod)(void* c, GGLuint tmu, const GGLSurface* surface);
// enable/disable features
void (*enable)(void* c,GGLenum name);
void (*disable)(void* c,GGLenum name);
void(*enableDisable)(void* c, GGLenum name, GGLboolean en);
// specify the fragment'scolor
void (*shadeModel)(void*c, GGLenum mode);
void (*color4xv)(void* c,const GGLclampx* color);
// specify color iterators(16.16)
void(*colorGrad12xv)(void* c, const GGLcolor* grad);
// specify Z coordinateiterators (0.32)
void (*zGrad3xv)(void* c,const GGLfixed32* grad);
// specify W coordinateiterators (16.16)
void (*wGrad3xv)(void* c,const GGLfixed* grad);
// specify fog iterator &color (16.16)
void (*fogGrad3xv)(void*c, const GGLfixed* grad);
void (*fogColor3xv)(void*c, const GGLclampx* color);
// specify blendingparameters
void (*blendFunc)(void* c,GGLenum src, GGLenum dst);
void(*blendFuncSeparate)(void* c, GGLenum src, GGLenum dst,
GGLenumsrcAlpha, GGLenum dstAplha);
// texture environnement(REPLACE / MODULATE / DECAL / BLEND)
void (*texEnvi)(void* c, GGLenum target,
GGLenumpname,
GGLintparam);
void (*texEnvxv)(void* c,GGLenum target,
GGLenum pname,const GGLfixed* params);
// texture parameters(Wrapping, filter)
void(*texParameteri)(void* c, GGLenum target,
GGLenumpname,
GGLintparam);
// texture iterators(16.16)
void (*texCoord2i)(void*c, GGLint s, GGLint t);
void (*texCoord2x)(void*c, GGLfixed s, GGLfixed t);
// s, dsdx, dsdy, scale,t, dtdx, dtdy, tscale
// This api uses blockfloating-point for S and T texture coordinates.
// All values are given in16.16, scaled by 'scale'. In other words,
// set scale to 0, for16.16 values.
void(*texCoordGradScale8xv)(void* c, GGLint tmu, const int32_t* grad8);
void (*texGeni)(void* c,GGLenum coord, GGLenum pname, GGLint param);
// masking
void (*colorMask)(void* c, GGLboolean red,
GGLbooleangreen,
GGLbooleanblue,
GGLbooleanalpha);
void (*depthMask)(void* c,GGLboolean flag);
void (*stencilMask)(void*c, GGLuint mask);
// alpha func
void (*alphaFuncx)(void*c, GGLenum func, GGLclampx ref);
// depth func
void (*depthFunc)(void* c,GGLenum func);
// logic op
void (*logicOp)(void* c,GGLenum opcode);
// clear
void (*clear)(void* c,GGLbitfield mask);
void (*clearColorx)(void*c,
GGLclampx r,GGLclampx g, GGLclampx b, GGLclampx a);
void (*clearDepthx)(void*c, GGLclampx depth);
void (*clearStencil)(void*c, GGLint s);
// framebuffer operations
void (*copyPixels)(void*c, GGLint x, GGLint y,
GGLsizei width,GGLsizei height, GGLenum type);
void (*rasterPos2x)(void*c, GGLfixed x, GGLfixed y);
void (*rasterPos2i)(void*c, GGLint x, GGLint y);
} GGLContext;
1.4 Pixelflinger的引用和释放
下面是pixelflinger的初始化函数和释放函数
system/core/libpixelflinger/pixelflinger.cpp
ssize_t gglInit(GGLContext**context)
{
void* const base =malloc(sizeof(context_t) + 32);
if (base) {
// always align thecontext on cache lines
context_t *c =(context_t *)((ptrdiff_t(base)+31) & ~0x1FL);
ggl_init_context(c);
c->base = base;
*context = (GGLContext*)c;
} else {
return -1;
}
return 0;
}
ssize_t gglUninit(GGLContext*con)
{
GGL_CONTEXT(c,(void*)con);
ggl_uninit_context(c);
free(c->base);
return 0;
}
gglInit 和 gglUninit是初opengl引用的，它们分别被引用的位置如下：
frameworks/base/opengl/libagl/texture.cpp
GGLContext*getRasterizer(ogles_context_t* c)
{
GGLContext* ggl =c->textures.ggl;
..
gglInit(&ggl);
…
}
voidogles_uninit_texture(ogles_context_t* c)
{
if (c->textures.ggl)
gglUninit(c->textures.ggl);
…
}
1.5 Pixelflinger支持的像素格式
voidggl_init_context(context_t* c)
{
...
c->formats =gglGetPixelFormatTable();
…
}
formats 指向pixelformat支持的像素格式表，该表在下面文件里:
system/core/libpixelflinger/format.cpp
const GGLFormat*gglGetPixelFormatTable(size_t* numEntries)
{
if (numEntries) {
*numEntries =sizeof(android::gPixelFormatInfos)/sizeof(GGLFormat);
}
returnandroid::gPixelFormatInfos;
}
static GGLFormat constgPixelFormatInfos[] =
{ // Alpha Red Green Blue
{ 0, 0, {{ 0, 0, 0, 0, 0, 0, 0, 0 }}, 0 }, // PIXEL_FORMAT_NONE
{ 4, 32, {{32,24, 8, 0, 16, 8, 24,16 }}, GGL_RGBA }, // PIXEL_FORMAT_RGBA_8888
{ 4, 24, {{ 0, 0, 8, 0, 16, 8, 24,16 }}, GGL_RGB }, // PIXEL_FORMAT_RGBX_8888
{ 3, 24, {{ 0, 0, 8, 0, 16, 8, 24,16 }}, GGL_RGB }, // PIXEL_FORMAT_RGB_888
{ 2, 16, {{ 0, 0, 16,11, 11, 5, 5, 0 }}, GGL_RGB }, // PIXEL_FORMAT_RGB_565
{ 4, 32, {{32,24, 24,16, 16, 8, 8, 0 }}, GGL_RGBA }, // PIXEL_FORMAT_BGRA_8888
{ 2, 16, {{ 1, 0, 16,11, 11, 6, 6, 1 }}, GGL_RGBA }, // PIXEL_FORMAT_RGBA_5551
{ 2, 16, {{ 4, 0, 16,12, 12, 8, 8, 4 }}, GGL_RGBA }, // PIXEL_FORMAT_RGBA_4444
{ 1, 8, {{ 8, 0, 0, 0, 0, 0, 0, 0 }}, GGL_ALPHA}, // PIXEL_FORMAT_A8
{ 1, 8, {{ 0, 0, 8, 0, 8, 0, 8, 0 }}, GGL_LUMINANCE},//PIXEL_FORMAT_L8
{ 2, 16, {{16, 8, 8, 0, 8, 0, 8, 0 }}, GGL_LUMINANCE_ALPHA},// PIXEL_FORMAT_LA_88
{ 1, 8, {{ 0, 0, 8, 5, 5, 2, 2, 0 }}, GGL_RGB }, // PIXEL_FORMAT_RGB_332
{ 0, 0, {{ 0, 0, 0, 0, 0, 0, 0, 0 }}, 0 }, // PIXEL_FORMAT_NONE
{ 0, 0, {{ 0, 0, 0, 0, 0, 0, 0, 0 }}, 0 }, // PIXEL_FORMAT_NONE
{ 0, 0, {{ 0, 0, 0, 0, 0, 0, 0, 0 }}, 0 }, // PIXEL_FORMAT_NONE
{ 0, 0, {{ 0, 0, 0, 0, 0, 0, 0, 0 }}, 0 }, // PIXEL_FORMAT_NONE
{ 1, 16, {{ 0, 8, 0, 8, 0, 8, 0, 0 }}, GGL_Y_CB_CR_SP },// PIXEL_FORMAT_YCbCr_422_SP
{ 1, 12, {{ 0, 8, 0, 8, 0, 8, 0, 0 }}, GGL_Y_CB_CR_SP },// PIXEL_FORMAT_YCbCr_420_SP
{ 1, 16, {{ 0, 8, 0, 8, 0, 8, 0, 0 }}, GGL_Y_CB_CR_P }, // PIXEL_FORMAT_YCbCr_422_P
{ 1, 12, {{ 0, 8, 0, 8, 0, 8, 0, 0 }}, GGL_Y_CB_CR_P }, // PIXEL_FORMAT_YCbCr_420_P
{ 1, 16, {{ 0, 8, 0, 8, 0, 8, 0, 0 }}, GGL_Y_CB_CR_I }, // PIXEL_FORMAT_YCbCr_422_I
{ 1, 12, {{ 0, 8, 0, 8, 0, 8, 0, 0 }}, GGL_Y_CB_CR_I }, // PIXEL_FORMAT_YCbCr_420_I
{ 0, 0, {{ 0, 0, 0, 0, 0, 0, 0, 0 }}, 0 }, // PIXEL_FORMAT_NONE
{ 0, 0, {{ 0, 0, 0, 0, 0, 0, 0, 0 }}, 0 }, // PIXEL_FORMAT_NONE
{ 2, 16, {{ 0, 0, 16, 0, 0, 0, 0, 0 }}, GGL_DEPTH_COMPONENT},
{ 1, 8, {{ 8, 0, 0, 0, 0, 0, 0, 0 }}, GGL_STENCIL_INDEX },
{ 4, 24, {{ 0, 0, 24, 0, 0, 0, 0, 0 }}, GGL_DEPTH_COMPONENT},
{ 4, 8, {{ 32,24, 0, 0, 0, 0, 0, 0 }}, GGL_STENCIL_INDEX },
};
1.6 Pixelflinger 接口
1.6.1 裁剪操作函数
void(*scissor)(void* c, GGLint x, GGLint y, GGLsizei width, GGLsizeiheight);
该函数的功能是设置裁剪范围：
c->state.scissor.left = x;
c->state.scissor.top = y;
c->state.scissor.right = width;
c->state.scissor.bottom= height;
1.6.2 纹理和色彩缓冲设置函数
void(*activeTexture)(void* c, GGLuint tmu);
该函数的功能是设置activeTexture索引及值：
c->activeTMUIndex= tmu;
c->activeTMU= &(c->state.texture[tmu]);
void(*bindTexture)(void* c, const GGLSurface* surface);
该函数的功能是将activeTMU的surface绑定到源surface：
ggl_set_surface(c,&(c->activeTMU->surface), surface);
void(*colorBuffer)(void* c, const GGLSurface* surface);
该函数的功能是将state.buffers.color 绑定到源surface：
ggl_set_surface(c,&(c->state.buffers.color), surface);
void(*readBuffer)(void* c, const GGLSurface* surface);
该函数的功能是将state.buffers.read 绑定到源surface：
ggl_set_surface(c,&(c->state.buffers.read), surface);
void(*depthBuffer)(void* c, const GGLSurface* surface);
该函数的功能是将state.buffers.depth.format初始化为GGL_PIXEL_FORMAT_NONE：
c->state.buffers.depth.format= GGL_PIXEL_FORMAT_NONE;
1.6.3 使能或禁止某种属性
Pixelflinger开放如下属性可供使能或禁止:
GGL_BLEND
混合使能：
if (enable) c->state.enables|= GGL_ENABLE_BLENDING;
else c->state.enables &= ~GGL_ENABLE_BLENDING;
GGL_SCISSOR_TEST
裁剪测试使能：
if (enable) c->state.enables|= GGL_ENABLE_SCISSOR_TEST;
else c->state.enables &= ~GGL_ENABLE_SCISSOR_TEST;
GGL_ALPHA_TEST
ALPHA测试使能:
if (enable) c->state.enables|= GGL_ENABLE_ALPHA_TEST;
else c->state.enables &= ~GGL_ENABLE_ALPHA_TEST;
GGL_COLOR_LOGIC_OP
顔色逻辑操作使能：
if (enable) c->state.enables|= GGL_ENABLE_LOGIC_OP;
else c->state.enables &= ~GGL_ENABLE_LOGIC_OP;
GGL_DITHER
抖动使能：
if (enable) c->state.enables|= GGL_ENABLE_DITHER;
else c->state.enables &= ~GGL_ENABLE_DITHER;
static voidenable_disable(context_t* c, GGLenum name, int en)
{
switch (name) {
case GGL_BLEND: ggl_enable_blending(c, en); break;
case GGL_SCISSOR_TEST: ggl_enable_scissor_test(c, en); break;
case GGL_ALPHA_TEST: ggl_enable_alpha_test(c, en); break;
case GGL_COLOR_LOGIC_OP: ggl_enable_logic_op(c, en); break;
case GGL_DITHER: ggl_enable_dither(c, en); break;
case GGL_STENCIL_TEST: ggl_enable_stencil_test(c, en); break;
case GGL_DEPTH_TEST: ggl_enable_depth_test(c, en); break;
case GGL_AA: ggl_enable_aa(c, en); break;
case GGL_TEXTURE_2D: ggl_enable_texture2d(c, en); break;
case GGL_W_LERP: ggl_enable_w_lerp(c, en); break;
case GGL_FOG: ggl_enable_fog(c, en); break;
caseGGL_POINT_SMOOTH_NICE: ggl_enable_point_aa_nice(c, en); break;
}
}
void (*enable)(void* c,GGLenum name);
该函数的功能是使用某种属性：
enable_disable(c, name, 1);
void(*disable)(void* c, GGLenum name);
该函数的功能是禁止某种属性：
enable_disable(c, name, 0);
void(*enableDisable)(void* c, GGLenum name, GGLboolean en);
该函数的功能是使用或禁止某种属性：
enable_disable(c, name, en ?1 : 0);
1.6.4 指定片段顔色
void(*shadeModel)(void* c, GGLenum mode);
该函数的功能是指定阴影模式，是FLAT还是SMOOTH：
caseGGL_FLAT:
if(c->state.enables & GGL_ENABLE_SMOOTH) {
c->state.enables&= ~GGL_ENABLE_SMOOTH;
ggl_state_changed(c,GGL_PIXEL_PIPELINE_STATE);
}
break;
caseGGL_SMOOTH:
if(!(c->state.enables & GGL_ENABLE_SMOOTH)) {
c->state.enables|= GGL_ENABLE_SMOOTH;
ggl_state_changed(c,GGL_PIXEL_PIPELINE_STATE);
}
void(*color4xv)(void* c, const GGLclampx* color);
该函数的功能是指定渐变的顔色：
c->shade.r0 =gglFixedToIteratedColor(color[0]);
c->shade.g0 =gglFixedToIteratedColor(color[1]);
c->shade.b0 =gglFixedToIteratedColor(color[2]);
c->shade.a0 =gglFixedToIteratedColor(color[3]);
1.6.5 迭代程序
void(*colorGrad12xv)(void* c, const GGLcolor* grad);
该函数的功能是指定渐变的顔色及顔色位置：
constint32_t round = 0x8000;
c->shade.r0 = grad[ 0] + round;
c->shade.drdx= grad[ 1];
c->shade.drdy= grad[ 2];
c->shade.g0 = grad[ 3] + round;
c->shade.dgdx= grad[ 4];
c->shade.dgdy= grad[ 5];
c->shade.b0 = grad[ 6] + round;
c->shade.dbdx= grad[ 7];
c->shade.dbdy= grad[ 8];
c->shade.a0 = grad[ 9] + round;
c->shade.dadx= grad[10];
c->shade.dady= grad[11];
void (*zGrad3xv)(void*c, const GGLfixed32* grad);
该函数的功能是指定渐变的Z轴值及Z值位置：
const uint32_t round =0x8000;
c->shade.z0 = grad[0] +round;
c->shade.dzdx = grad[1];
c->shade.dzdy = grad[2];
void (*wGrad3xv)(void*c, const GGLfixed* grad);
该函数的功能是指定渐变的W轴值及W值位置：
const uint32_t round =0x8000;
c->shade.z0 = grad[0] +round;
c->shade.dzdx = grad[1];
c->shade.dzdy = grad[2];
void(*fogGrad3xv)(void* c, const GGLfixed* grad);
该函数的功能是指定渐变的雾化值：
c->shade.f0 = grad[0];
c->shade.dfdx = grad[1];
c->shade.dfdy = grad[2];
void(*fogColor3xv)(void* c, const GGLclampx* color);
该函数的功能是指定雾化顔色：
c->state.fog.color[GGLFormat::RED] = (r - (r>>8))>>8;
c->state.fog.color[GGLFormat::GREEN]=(g - (g>>8))>>8;
c->state.fog.color[GGLFormat::BLUE]= (b - (b>>8))>>8;
1.6.6 指定混合参数
void(*blendFunc)(void* c, GGLenum src, GGLenum dst);
该函数的功能是指定混合源和混合目的地，同src和src_alpha一致,dst和dst_alpha一致：
c->state.blend.src = src;
c->state.blend.src_alpha= src;
c->state.blend.dst =dst;
c->state.blend.dst_alpha= dst;
c->state.blend.alpha_separate= 0;
void(*blendFuncSeparate)(void* c, GGLenum src, GGLenum dst,
GGLenumsrcAlpha, GGLenum dstAplha);
该函数的功能是指定混合源和混合目的地，同src和src_alpha分开,dst和dst_alpha分开：
c->state.blend.src = src;
c->state.blend.src_alpha= srcAlpha;
c->state.blend.dst =dst;
c->state.blend.dst_alpha= dstAplha;
c->state.blend.alpha_separate= 1;
1.6.7 指定纹理参数
void (*texEnvi)(void*c, GGLenum target,
GGLenumpname,
GGLintparam);
该函数的功能是指定纹理环境参数：
case GGL_REPLACE:
case GGL_MODULATE:
case GGL_DECAL:
case GGL_BLEND:
case GGL_ADD:
if (c->activeTMU->env!= param) {
c->activeTMU->env= param;
void(*texEnvxv)(void* c, GGLenum target,
GGLenumpname, const GGLfixed* params);
该函数的功能是指定纹理环境模式：
switch (pname) {
case GGL_TEXTURE_ENV_MODE:
ggl_texEnvi(con,target, pname, params[0]);
break;
caseGGL_TEXTURE_ENV_COLOR: {
uint8_t* const color =c->activeTMU->env_color;
const GGLclampx r =gglClampx(params[0]);
const GGLclampx g =gglClampx(params[1]);
const GGLclampx b =gglClampx(params[2]);
const GGLclampx a =gglClampx(params[3]);
color[0] =(a-(a>>8))>>8;
color[1] =(r-(r>>8))>>8;
color[2] =(g-(g>>8))>>8;
color[3] =(b-(b>>8))>>8;
break;
}
void(*texParameteri)(void* c, GGLenum target,
GGLenumpname,
GGLintparam);
该函数的功能是指定纹理参数：
switch (pname) {
case GGL_TEXTURE_WRAP_S:
what =&c->activeTMU->s_wrap;
case GGL_TEXTURE_WRAP_T:
caseGGL_TEXTURE_MIN_FILTER:
caseGGL_TEXTURE_MAG_FILTER:
*what = param;
void(*texCoord2x)(void* c, GGLfixed s, GGLfixed t);
该函数的功能是设置纹理渐变的s和t：
c->activeTMU->shade.is0= s;
c->activeTMU->shade.it0= t;
c->activeTMU->shade.sscale=0;
c->activeTMU->shade.tscale=0;
void(*texCoordGradScale8xv)(void* c, GGLint tmu, const int32_t* grad8);
该函数的功能是设置渐变的S、T以及SCALE：
texture_t& u =c->state.texture[tmu];
u.shade.is0 = grad[0];
u.shade.idsdx = grad[1];
u.shade.idsdy = grad[2];
u.shade.it0 = grad[3];
u.shade.idtdx = grad[4];
u.shade.idtdy = grad[5];
u.shade.sscale= grad[6];
u.shade.tscale= grad[7];
void(*texGeni)(void* c, GGLenum coord, GGLenum pname, GGLint param);
该函数的功能是设置 S和 T 的参数：
if (coord == GGL_S) coord_ptr = &(c->activeTMU->s_coord);
else if (coord == GGL_T) coord_ptr = &(c->activeTMU->t_coord);
*coord_ptr = uint32_t(param);
1.6.8 屏蔽函数
void (*colorMask)(void*c, GGLboolean red,
GGLbooleangreen,
GGLbooleanblue,
GGLbooleanalpha);
该函数的功能是设置顔色掩码：
if (a) mask |= 1 <<GGLFormat::ALPHA;
if (r) mask |= 1 <<GGLFormat::RED;
if (g) mask |= 1 <<GGLFormat::GREEN;
if (b) mask |= 1 <<GGLFormat::BLUE;
c->state.mask.color= mask;
void(*depthMask)(void* c, GGLboolean flag);
该函数的功能是设置深度掩码：
c->state.mask.depth =flag?1:0;
void(*stencilMask)(void* c, GGLuint mask);
该函数的功能是设置蜡版掩码：
c->state.mask.stencil =mask;