Matrix
Android android.graphics.Matrix 类是一个3 x 3的矩阵
源码
frameworks/base/graphics/java/android/graphics/Matrix.java
/**
* The Matrix class holds a 3x3 matrix for transforming coordinates.
*/
public class Matrix {
/**
* Create an identity matrix
*/
public Matrix() {
native_instance = native_create(0);
}
/**
* Create a matrix that is a (deep) copy of src
* @param src The matrix to copy into this matrix
*/
public Matrix(Matrix src) {
native_instance = native_create(src != null ? src.native_instance : 0);
}
/**
* Set the matrix to scale by sx and sy, with a pivot point at (px, py).
* The pivot point is the coordinate that should remain unchanged by the
* specified transformation.
*/
public void setScale(float sx, float sy, float px, float py) {
native_setScale(native_instance, sx, sy, px, py);
}
private static native long native_create(long native_src_or_zero);
private static native void native_setScale(long native_object,
float sx, float sy, float px, float py);
}
矩阵乘法
注意：矩阵的乘法不满足交换律
矩阵变换
| 英文 | 中文 |
|---|---|
| Translate | 位移 |
| Rotate | 旋转 |
| Scale | 缩放 |
| Skew | 错切 |
位移
对应 MTRANS_X 与 MTRANS_Y
位移操作是指将坐标（x0,y0）平移一定的距离，我们直接将坐标加上平移的距离即可得到平移后的坐标：
/** Set the matrix to translate by (dx, dy). */
public void setTranslate(float dx, float dy) {
native_setTranslate(native_instance, dx, dy);
}
/**
* Preconcats the matrix with the specified translation.
* M' = M * T(dx, dy)
*/
public boolean preTranslate(float dx, float dy) {
native_preTranslate(native_instance, dx, dy);
return true;
}
/**
* Postconcats the matrix with the specified translation.
* M' = T(dx, dy) * M
*/
public boolean postTranslate(float dx, float dy) {
native_postTranslate(native_instance, dx, dy);
return true;
}
缩放
对应 MSCALE_X 与 MSCALE_Y
假设对某个点宽度缩放 k1 倍，高度缩放 k2 倍，该点坐标为 x0、y0，缩放后坐标为 x、y，那么缩放的公式如下：
/**
* Set the matrix to scale by sx and sy, with a pivot point at (px, py).
* The pivot point is the coordinate that should remain unchanged by the
* specified transformation.
*/
public void setScale(float sx, float sy, float px, float py) {
native_setScale(native_instance, sx, sy, px, py);
}
/**
* Preconcats the matrix with the specified scale.
* M' = M * S(sx, sy, px, py)
*/
public boolean preScale(float sx, float sy, float px, float py) {
native_preScale(native_instance, sx, sy, px, py);
return true;
}
/**
* Postconcats the matrix with the specified scale.
* M' = S(sx, sy, px, py) * M
*/
public boolean postScale(float sx, float sy, float px, float py) {
native_postScale(native_instance, sx, sy, px, py);
return true;
}
相机缩放
相机预览比例和相机比例一致, 保持中心点坐标不动进行缩放
Matrix matrix = new Matrix();
matrix = mPreview.getTransform(matrix);
float scaleX = 1f, scaleY = 1f;
float scaledTextureWidth, scaledTextureHeight;
if (mWidth > mHeight * mAspectRatio) {
scaledTextureWidth = mHeight * mAspectRatio;
scaledTextureHeight = mHeight;
} else {
scaledTextureWidth = mWidth;
scaledTextureHeight = mWidth / mAspectRatio;
}
scaleX = scaledTextureWidth / mWidth;
scaleY = scaledTextureHeight / mHeight;
matrix.setScale(scaleX, scaleY, (float) mWidth / 2, (float) mHeight / 2);
错切
对应 MSKEW_X 与 MSKEW_Y
/**
* Set the matrix to skew by sx and sy, with a pivot point at (px, py).
* The pivot point is the coordinate that should remain unchanged by the
* specified transformation.
*/
public void setSkew(float kx, float ky, float px, float py) {
native_setSkew(native_instance, kx, ky, px, py);
}
/**
* Preconcats the matrix with the specified skew.
* M' = M * K(kx, ky, px, py)
*/
public boolean preSkew(float kx, float ky, float px, float py) {
native_preSkew(native_instance, kx, ky, px, py);
return true;
}
/**
* Postconcats the matrix with the specified skew.
* M' = K(kx, ky, px, py) * M
*/
public boolean postSkew(float kx, float ky, float px, float py) {
native_postSkew(native_instance, kx, ky, px, py);
return true;
}
旋转
旋转相对以上三种变化又有一点复杂，这里涉及一些三角函数的计算
/**
* Set the matrix to rotate by the specified number of degrees, with a pivot
* point at (px, py). The pivot point is the coordinate that should remain
* unchanged by the specified transformation.
*/
public void setRotate(float degrees, float px, float py) {
native_setRotate(native_instance, degrees, px, py);
}
/**
* Preconcats the matrix with the specified rotation.
* M' = M * R(degrees, px, py)
*/
public boolean preRotate(float degrees, float px, float py) {
native_preRotate(native_instance, degrees, px, py);
return true;
}
/**
* Postconcats the matrix with the specified rotation.
* M' = R(degrees) * M
*/
public boolean postRotate(float degrees) {
native_postRotate(native_instance, degrees);
return true;
}
JNI
frameworks/base/libs/hwui/Matrix.cpp
#include "GraphicsJNI.h"
#include "Matrix.h"
#include "SkMatrix.h"
#include "core_jni_helpers.h"
#include <Caches.h>
#include <jni.h>
static const JNINativeMethod methods[] = {
{"finalizer", "(J)V", (void*) SkMatrixGlue::finalizer},
{"native_create","(J)J", (void*) SkMatrixGlue::create},
{"native_isIdentity","!(J)Z", (void*) SkMatrixGlue::isIdentity},
{"native_isAffine","!(J)Z", (void*) SkMatrixGlue::isAffine},
{"native_rectStaysRect","!(J)Z", (void*) SkMatrixGlue::rectStaysRect},
{"native_reset","!(J)V", (void*) SkMatrixGlue::reset},
{"native_set","!(JJ)V", (void*) SkMatrixGlue::set},
{"native_setTranslate","!(JFF)V", (void*) SkMatrixGlue::setTranslate},
{"native_setScale","!(JFFFF)V", (void*) SkMatrixGlue::setScale__FFFF},
{"native_setScale","!(JFF)V", (void*) SkMatrixGlue::setScale__FF},
{"native_setRotate","!(JFFF)V", (void*) SkMatrixGlue::setRotate__FFF},
{"native_setRotate","!(JF)V", (void*) SkMatrixGlue::setRotate__F},
{"native_setSinCos","!(JFFFF)V", (void*) SkMatrixGlue::setSinCos__FFFF},
{"native_setSinCos","!(JFF)V", (void*) SkMatrixGlue::setSinCos__FF},
{"native_setSkew","!(JFFFF)V", (void*) SkMatrixGlue::setSkew__FFFF},
{"native_setSkew","!(JFF)V", (void*) SkMatrixGlue::setSkew__FF},
{"native_setConcat","!(JJJ)V", (void*) SkMatrixGlue::setConcat},
{"native_preTranslate","!(JFF)V", (void*) SkMatrixGlue::preTranslate},
{"native_preScale","!(JFFFF)V", (void*) SkMatrixGlue::preScale__FFFF},
{"native_preScale","!(JFF)V", (void*) SkMatrixGlue::preScale__FF},
{"native_preRotate","!(JFFF)V", (void*) SkMatrixGlue::preRotate__FFF},
{"native_preRotate","!(JF)V", (void*) SkMatrixGlue::preRotate__F},
{"native_preSkew","!(JFFFF)V", (void*) SkMatrixGlue::preSkew__FFFF},
{"native_preSkew","!(JFF)V", (void*) SkMatrixGlue::preSkew__FF},
{"native_preConcat","!(JJ)V", (void*) SkMatrixGlue::preConcat},
{"native_postTranslate","!(JFF)V", (void*) SkMatrixGlue::postTranslate},
{"native_postScale","!(JFFFF)V", (void*) SkMatrixGlue::postScale__FFFF},
{"native_postScale","!(JFF)V", (void*) SkMatrixGlue::postScale__FF},
{"native_postRotate","!(JFFF)V", (void*) SkMatrixGlue::postRotate__FFF},
{"native_postRotate","!(JF)V", (void*) SkMatrixGlue::postRotate__F},
{"native_postSkew","!(JFFFF)V", (void*) SkMatrixGlue::postSkew__FFFF},
{"native_postSkew","!(JFF)V", (void*) SkMatrixGlue::postSkew__FF},
{"native_postConcat","!(JJ)V", (void*) SkMatrixGlue::postConcat},
{"native_setRectToRect","!(JLandroid/graphics/RectF;Landroid/graphics/RectF;I)Z", (void*) SkMatrixGlue::setRectToRect},
{"native_setPolyToPoly","!(J[FI[FII)Z", (void*) SkMatrixGlue::setPolyToPoly},
{"native_invert","!(JJ)Z", (void*) SkMatrixGlue::invert},
{"native_mapPoints","!(J[FI[FIIZ)V", (void*) SkMatrixGlue::mapPoints},
{"native_mapRect","!(JLandroid/graphics/RectF;Landroid/graphics/RectF;)Z", (void*) SkMatrixGlue::mapRect__RectFRectF},
{"native_mapRadius","!(JF)F", (void*) SkMatrixGlue::mapRadius},
{"native_getValues","!(J[F)V", (void*) SkMatrixGlue::getValues},
{"native_setValues","!(J[F)V", (void*) SkMatrixGlue::setValues},
{"native_equals", "!(JJ)Z", (void*) SkMatrixGlue::equals}
};
Skia
./external/skia/src/core/SkMatrix.cpp
SkMatrix.h
SkScalar fMat[9];
enum {
kMScaleX,
kMSkewX,
kMTransX,
kMSkewY,
kMScaleY,
kMTransY,
kMPersp0,
kMPersp1,
kMPersp2
};
