static SkString sweepCode(const SkShader::GradientInfo& info) {
SkString function("{exch atan 360 div\n");
tileModeCode(info.fTileMode, &function);
gradientFunctionCode(info, &function);
function.append("}");
return function;
}
static SkString linearCode(const SkShader::GradientInfo& info) {
SkString function("{pop\n"); // Just ditch the y value.
tileModeCode(info.fTileMode, &function);
gradientFunctionCode(info, &function);
function.append("}");
return function;
}
static void sweepCode(const SkShader::GradientInfo& info,
const SkMatrix& perspectiveRemover,
SkDynamicMemoryWStream* function) {
function->writeText("{exch atan 360 div\n");
tileModeCode((SkTileMode)info.fTileMode, function);
gradient_function_code(info, function);
function->writeText("}");
}
static SkString linearCode(const SkShader::GradientInfo& info,
const SkMatrix& perspectiveRemover) {
SkString function("{");
function.append(apply_perspective_to_coordinates(perspectiveRemover));
function.append("pop\n"); // Just ditch the y value.
tileModeCode(info.fTileMode, &function);
gradientFunctionCode(info, &function);
function.append("}");
return function;
}
static void linearCode(const SkShader::GradientInfo& info,
const SkMatrix& perspectiveRemover,
SkDynamicMemoryWStream* function) {
function->writeText("{");
apply_perspective_to_coordinates(perspectiveRemover, function);
function->writeText("pop\n"); // Just ditch the y value.
tileModeCode((SkTileMode)info.fTileMode, function);
gradient_function_code(info, function);
function->writeText("}");
}
static SkString radialCode(const SkShader::GradientInfo& info) {
SkString function("{");
// Find the distance from the origin.
function.append("dup " // x y y
"mul " // x y^2
"exch " // y^2 x
"dup " // y^2 x x
"mul " // y^2 x^2
"add " // y^2+x^2
"sqrt\n"); // sqrt(y^2+x^2)
tileModeCode(info.fTileMode, &function);
gradientFunctionCode(info, &function);
function.append("}");
return function;
}
/* The math here is all based on the description in Two_Point_Radial_Gradient,
with one simplification, the coordinate space has been scaled so that
Dr = 1. This means we don't need to scale the entire equation by 1/Dr^2.
*/
static SkString twoPointRadialCode(const SkShader::GradientInfo& info,
const SkMatrix& perspectiveRemover) {
SkScalar dx = info.fPoint[0].fX - info.fPoint[1].fX;
SkScalar dy = info.fPoint[0].fY - info.fPoint[1].fY;
SkScalar sr = info.fRadius[0];
SkScalar a = SkScalarMul(dx, dx) + SkScalarMul(dy, dy) - SK_Scalar1;
bool posRoot = info.fRadius[1] > info.fRadius[0];
// We start with a stack of (x y), copy it and then consume one copy in
// order to calculate b and the other to calculate c.
SkString function("{");
function.append(apply_perspective_to_coordinates(perspectiveRemover));
function.append("2 copy ");
// Calculate -b and b^2.
function.appendScalar(dy);
function.append(" mul exch ");
function.appendScalar(dx);
function.append(" mul add ");
function.appendScalar(sr);
function.append(" sub 2 mul neg dup dup mul\n");
// Calculate c
function.append("4 2 roll dup mul exch dup mul add ");
function.appendScalar(SkScalarMul(sr, sr));
function.append(" sub\n");
// Calculate the determinate
function.appendScalar(SkScalarMul(SkIntToScalar(4), a));
function.append(" mul sub abs sqrt\n");
// And then the final value of t.
if (posRoot) {
function.append("sub ");
} else {
function.append("add ");
}
function.appendScalar(SkScalarMul(SkIntToScalar(2), a));
function.append(" div\n");
tileModeCode(info.fTileMode, &function);
gradientFunctionCode(info, &function);
function.append("}");
return function;
}
static SkString radialCode(const SkShader::GradientInfo& info,
const SkMatrix& perspectiveRemover) {
SkString function("{");
function.append(apply_perspective_to_coordinates(perspectiveRemover));
// Find the distance from the origin.
function.append("dup " // x y y
"mul " // x y^2
"exch " // y^2 x
"dup " // y^2 x x
"mul " // y^2 x^2
"add " // y^2+x^2
"sqrt\n"); // sqrt(y^2+x^2)
tileModeCode(info.fTileMode, &function);
gradientFunctionCode(info, &function);
function.append("}");
return function;
}
static void radialCode(const SkShader::GradientInfo& info,
const SkMatrix& perspectiveRemover,
SkDynamicMemoryWStream* function) {
function->writeText("{");
apply_perspective_to_coordinates(perspectiveRemover, function);
// Find the distance from the origin.
function->writeText("dup " // x y y
"mul " // x y^2
"exch " // y^2 x
"dup " // y^2 x x
"mul " // y^2 x^2
"add " // y^2+x^2
"sqrt\n"); // sqrt(y^2+x^2)
tileModeCode((SkTileMode)info.fTileMode, function);
gradient_function_code(info, function);
function->writeText("}");
}
/* Conical gradient shader, based on the Canvas spec for radial gradients
See: http://www.w3.org/TR/2dcontext/#dom-context-2d-createradialgradient
*/
static SkString twoPointConicalCode(const SkShader::GradientInfo& info,
const SkMatrix& perspectiveRemover) {
SkScalar dx = info.fPoint[1].fX - info.fPoint[0].fX;
SkScalar dy = info.fPoint[1].fY - info.fPoint[0].fY;
SkScalar r0 = info.fRadius[0];
SkScalar dr = info.fRadius[1] - info.fRadius[0];
SkScalar a = SkScalarMul(dx, dx) + SkScalarMul(dy, dy) -
SkScalarMul(dr, dr);
// First compute t, if the pixel falls outside the cone, then we'll end
// with 'false' on the stack, otherwise we'll push 'true' with t below it
// We start with a stack of (x y), copy it and then consume one copy in
// order to calculate b and the other to calculate c.
SkString function("{");
function.append(apply_perspective_to_coordinates(perspectiveRemover));
function.append("2 copy ");
// Calculate b and b^2; b = -2 * (y * dy + x * dx + r0 * dr).
function.appendScalar(dy);
function.append(" mul exch ");
function.appendScalar(dx);
function.append(" mul add ");
function.appendScalar(SkScalarMul(r0, dr));
function.append(" add -2 mul dup dup mul\n");
// c = x^2 + y^2 + radius0^2
function.append("4 2 roll dup mul exch dup mul add ");
function.appendScalar(SkScalarMul(r0, r0));
function.append(" sub dup 4 1 roll\n");
// Contents of the stack at this point: c, b, b^2, c
// if a = 0, then we collapse to a simpler linear case
if (a == 0) {
// t = -c/b
function.append("pop pop div neg dup ");
// compute radius(t)
function.appendScalar(dr);
function.append(" mul ");
function.appendScalar(r0);
function.append(" add\n");
// if r(t) < 0, then it's outside the cone
function.append("0 lt {pop false} {true} ifelse\n");
} else {
// quadratic case: the Canvas spec wants the largest
// root t for which radius(t) > 0
// compute the discriminant (b^2 - 4ac)
function.appendScalar(SkScalarMul(SkIntToScalar(4), a));
function.append(" mul sub dup\n");
// if d >= 0, proceed
function.append("0 ge {\n");
// an intermediate value we'll use to compute the roots:
// q = -0.5 * (b +/- sqrt(d))
function.append("sqrt exch dup 0 lt {exch -1 mul} if");
function.append(" add -0.5 mul dup\n");
// first root = q / a
function.appendScalar(a);
function.append(" div\n");
// second root = c / q
function.append("3 1 roll div\n");
// put the larger root on top of the stack
function.append("2 copy gt {exch} if\n");
// compute radius(t) for larger root
function.append("dup ");
function.appendScalar(dr);
function.append(" mul ");
function.appendScalar(r0);
function.append(" add\n");
// if r(t) > 0, we have our t, pop off the smaller root and we're done
function.append(" 0 gt {exch pop true}\n");
// otherwise, throw out the larger one and try the smaller root
function.append("{pop dup\n");
function.appendScalar(dr);
function.append(" mul ");
function.appendScalar(r0);
function.append(" add\n");
// if r(t) < 0, push false, otherwise the smaller root is our t
function.append("0 le {pop false} {true} ifelse\n");
function.append("} ifelse\n");
// d < 0, clear the stack and push false
function.append("} {pop pop pop false} ifelse\n");
}
// if the pixel is in the cone, proceed to compute a color
function.append("{");
tileModeCode(info.fTileMode, &function);
gradientFunctionCode(info, &function);
// otherwise, just write black
function.append("} {0 0 0} ifelse }");
return function;
}
