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Commit e01fc2c7 authored by Chia-I Wu's avatar Chia-I Wu
Browse files

renderengine: avoid divide-by-zero in shaders 

We have

   max(1e-6, color.y)

to make sure the divisor is non-zero.  But when mediump means
half-precision floats, 1e-6 is smaller than the minimum positive
normal number.  The line might have no effect at all.

This is noticed when looking into the referenced bug.

Bug: 116864006
Test: manual
Change-Id: Ic39209e19ceeba6f51688dc9549746bf0f6a98e1
parent 3a4f401b

services/surfaceflinger/RenderEngine/gl/ProgramCache.cpp

+7 −5
Original line number Diff line number Diff line
@@ -316,7 +316,7 @@ void ProgramCache::generateToneMappingProcess(Formatter& fs, const Key& needs) { 


                            // scale [0.0, maxInLumi] to [0.0, maxOutLumi]

                            if (maxInLumi <= maxOutLumi) {

                                nits *= maxOutLumi / maxInLumi;

                                return color * (maxOutLumi / maxInLumi);

                            } else {

                                // three control points

                                const float x0 = 10.0;
@@ -337,7 +337,7 @@ void ProgramCache::generateToneMappingProcess(Formatter& fs, const Key& needs) { 
                                if (nits < x0) {

                                    // scale [0.0, x0] to [0.0, y0] linearly

                                    float slope = y0 / x0;

                                    nits *= slope;

                                    return color * slope;

                                } else if (nits < x1) {

                                    // scale [x0, x1] to [y0, y1] linearly

                                    float slope = (y1 - y0) / (x1 - x0);
@@ -355,7 +355,8 @@ void ProgramCache::generateToneMappingProcess(Formatter& fs, const Key& needs) { 
                                }

                            }



                            return color * (nits / max(1e-6, color.y));

                            // color.y is greater than x0 and is thus non-zero

                            return color * (nits / color.y);

                        }

                    )__SHADER__";

                    break;
@@ -386,7 +387,7 @@ void ProgramCache::generateToneMappingProcess(Formatter& fs, const Key& needs) { 
                    if (nits <= x0) {

                        // scale [0.0, x0] to [0.0, y0] linearly

                        const float slope = y0 / x0;

                        nits *= slope;

                        return color * slope;

                    } else if (nits <= x1) {

                        // scale [x0, x1] to [y0, y1] using a curve

                        float t = (nits - x0) / (x1 - x0);
@@ -401,7 +402,8 @@ void ProgramCache::generateToneMappingProcess(Formatter& fs, const Key& needs) { 
                        nits = (1.0 - t) * (1.0 - t) * y2 + 2.0 * (1.0 - t) * t * c3 + t * t * y3;

                    }



                    return color * (nits / max(1e-6, color.y));

                    // color.y is greater than x0 and is thus non-zero

                    return color * (nits / color.y);

                }

            )__SHADER__";

            break;