Bug 1731758 - Avoid Adreno 3xx driver bug in brush_blend shader. r=gfx-reviewers,nical

// This function has to be factored out due to the following issue:

// https://github.com/servo/webrender/wiki/Driver-issues#bug-1532245---switch-statement-inside-control-flow-inside-switch-statement-fails-to-compile-on-some-android-phones

// (and now the words "default: default:" so angle_shader_validation.rs passes)

vec4 ComponentTransfer(vec4 colora, ivec4 vfuncs, int table_address) {

vec4 ComponentTransfer(vec4 colora, int vfuncs, int table_address) {

    // We push a different amount of data to the gpu cache depending on the

    // function type.

    // Identity => 0 blocks

    vec4 texel;

    int k;

    // Dynamically indexing a vector is buggy on some platforms, so use a temporary array

    int[4] funcs = int[4](vfuncs.r, vfuncs.g, vfuncs.b, vfuncs.a);

    for (int i = 0; i < 4; i++) {

        switch (funcs[i]) {

        // Each function value is packed in to 4 bits, with the "r" function at bits 15-12

        // and the "a" function at bits 3-0.

        int func = (vfuncs >> (12 - (i * 4))) & 0xf;

        switch (func) {

            case COMPONENT_TRANSFER_IDENTITY:

                break;

            case COMPONENT_TRANSFER_TABLE:

    int table_address,

    vec4 color_offset,

    mat4 color_mat,

    ivec4 v_funcs,

    int v_funcs,

    out vec3 color,

    out float alpha

) {

#define v_table_address v_op_table_address_vec.y

flat varying mat4 v_color_mat;

flat varying ivec4 v_funcs;

// The function to use for each component of a component transfer filter. Using a int[4]

// or vec4 (with each element or component containing the function for each component) has

// ran in to bugs 1695912 and 1731758, so instead we pack each value in to 4 bits of an

// integer. However, due to bug 1630356 we cannot simply use an int, so instead use the

// x component of an ivec2.

flat varying ivec2 v_funcs;

flat varying vec4 v_color_offset;

#ifdef WR_VERTEX_SHADER

    float amount = float(prim_user_data.z) / 65536.0;

    v_op = prim_user_data.y & 0xffff;

    v_funcs.x = (prim_user_data.y >> 16) & 0xffff;

    v_amount = amount;

    // This assignment is only used for component transfer filters but this

    // assignment has to be done here and not in the component transfer case

    // below because it doesn't get executed on Windows because of a suspected

    // miscompile of this shader on Windows. See

    // https://github.com/servo/webrender/wiki/Driver-issues#bug-1505871---assignment-to-varying-flat-arrays-inside-switch-statement-of-vertex-shader-suspected-miscompile-on-windows

    // default: just to satisfy angle_shader_validation.rs which needs one

    // default: for every switch, even in comments.

    v_funcs.r = (prim_user_data.y >> 28) & 0xf; // R

    v_funcs.g = (prim_user_data.y >> 24) & 0xf; // G

    v_funcs.b = (prim_user_data.y >> 20) & 0xf; // B

    v_funcs.a = (prim_user_data.y >> 16) & 0xf; // A

    SetupFilterParams(

        v_op,

        amount,

        v_table_address,

        v_color_offset,

        v_color_mat,

        v_funcs,

        v_funcs.x,

        color,

        alpha

    );