矩阵 - 在底部左侧旋转一个矩形，原点位于中心

Question

我正在做一些OpenGL编程，绘制2D矩形。我使用的是OpenGL ES 2.0，所以我不能使用glTranslate/glRotate等等，不得不推出我自己的矩阵。我希望能够为它们设置旋转和缩放值，缩放或旋转的起点取决于'halignment'和'valignment'。这段代码对于旋转正常工作（但是x，y坐标似乎还是有点偏离），但是我怎样才能使缩放工作？它似乎仍然希望使用左下角作为原点。

vid.xratio/vid.yratio是当前屏幕与本地坐标系中x，y，宽度和高度传入的比率。例如，如果本地坐标基于640x480的网格，但你的屏幕当前是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

想通了......这里是正确的代码的情况下，它可以帮助别人

注意，我删除了引用vid.xratio和vid.yratio ......我做什么，而不是，在投影矩阵上调用Matrix :: Ortho之后，我会这样做：

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);