矩阵 - 旋转原点位于左下角的矩形，就好像原点位于中心一样

Question

我正在做一些 OpenGL 编程，绘制 2D 矩形。我正在使用 OpenGL ES 2.0，所以我不能使用 glTranslate/glRotate 等......必须滚动我自己的矩阵。我希望能够为它们设置旋转和缩放值，缩放或旋转的原点根据“对齐”和“对齐”而变化。这段代码对于旋转来说可以正确工作（但是 x，y 坐标似乎仍然有点偏差），但是我怎样才能让缩放工作呢？看来还是想以左下为原点。

vid.xratio/vid.yratio 是当前屏幕与传入的 x、y、宽度和高度的本地坐标系的比率。例如，如果本地坐标基于 640x480 网格，但你的屏幕当前为 1600x1200，坐标 (238, 185) 将是 (595, 462.5)。

const byte picVerts[] = {0, 0, 1, 0, 1, 1, 0, 1};
//
// DrawPictureSize
//
// Draws a picture on the 2D screen, width and height specified.
//
void DrawPictureSize(float x, float y, float width, float height, float scalex, float scaley, Vector::vector_t *upVec, byte alpha, Texture::texture_t *texture, int halignment, int valignment)
{
    if (!texture)
        return;

    float matrix[16];
    Matrix::LoadIdentity(matrix);

    width *= scalex * vid.xratio;
    height *= scaley * vid.yratio;

    float angle = U_Rad2Deg(atan2(upVec->y, upVec->x)) - 90;

    float xalign = 0;
    float yalign = 0;

    // Move into position
    if (halignment == Font::HALIGN_CENTER)
        xalign = width/2;
    else if (halignment == Font::HALIGN_RIGHT)
        xalign = width;
    if (valignment == Font::VALIGN_CENTER)
        yalign = height/2;
    else if (valignment == Font::VALIGN_TOP)
        yalign = height;

    // Move into position
    Matrix::Translate(matrix, x * vid.xratio, y * vid.yratio, 0.0f);

    // Translate to the origin before doing scaling/rotation
    Matrix::Translate(matrix, xalign, yalign, 0);
    Matrix::Rotate(matrix, angle, 0, 0, 1);
    Matrix::Translate(matrix, -xalign, -yalign, 0);

    // Expand square to image size
    Matrix::Scale(matrix, width, height, 1.0f);

Answer 1

弄清楚了...这是正确的代码，以防它对其他人有帮助

请注意，我删除了对 vid.xratio 和 vid.yratio 的引用...我所做的是在投影矩阵上调用 Matrix::Ortho 之后，我做：

Matrix::Scale(projMatrix, vid.xratio, vid.yratio, 1.0f);

const byte picVerts[] = {0, 0, 1, 0, 1, 1, 0, 1};
//
// DrawPictureSize
//
// Draws a picture on the 2D screen, width and height specified.
//
// Note: 'Set2D' must be called before this!
//
void DrawPictureSize(float x, float y, float width, float height, float scalex, float scaley, Vector::vector_t *upVec, byte alpha, Texture::texture_t *texture, int halignment, int valignment)
{
    if (!texture)
        return;

    float matrix[16];
    Matrix::LoadIdentity(matrix);

    width *= scalex;
    height *= scaley;

    float angle = U_Rad2Deg(atan2(upVec->y, upVec->x)) - 90;

    float xalign = 0;
    float yalign = 0;

    // Move into position
    if (halignment == Font::HALIGN_CENTER)
        xalign = width/2;
    else if (halignment == Font::HALIGN_RIGHT)
        xalign = width;
    if (valignment == Font::VALIGN_CENTER)
        yalign = height/2;
    else if (valignment == Font::VALIGN_TOP)
        yalign = height;

    // Move into position
    Matrix::Translate(matrix, x - xalign, y - yalign, 0.0f);

    // Translate to the origin before doing rotation
    if (angle != 0.0f)
    {
        Matrix::Translate(matrix, xalign, yalign, 0);
        Matrix::Rotate(matrix, angle, 0, 0, 1);
        Matrix::Translate(matrix, -xalign, -yalign, 0);
    }

    // Expand square to image size
    Matrix::Scale(matrix, width, height, 1.0f);