opengl - how to rotate and translate rectangle texture in shader -

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i'm trying handle transform of texture in fragment shader. resolution of window (640,360), rotation 30 degree, , scale vec2(0.5,0.5).

this want: correct result here fragment shader:

precision mediump float;                             varying vec2 v_texcoord;                            uniform sampler2d s_texture;                        mat3 maketranslation(vec2 t) {       mat3 m = mat3(1.0, 0.0, 0.0, 0.0, 1.0, 0.0, t.x, t.y, 1.0);     return m; }    mat3 makerotation( float angleinradians ){     float c = cos(angleinradians);     float s = sin(angleinradians);     mat3 m = mat3(c, -s, 0, s, c, 0, 0, 0, 1);     return m; } mat3 makescale(vec2 s) {    mat3 m = mat3( s.x, 0, 0, 0, s.y, 0, 0, 0, 1);     return m; }  void main(){     vec2 position = vec2(0.0,0.0);       vec2 scale = vec2(0.5,0.5);       float rotation = 30.0;       float r = rotation/180.0*3.14159;      vec2 size = vec2(640.0,480.0);      mat3 mt = maketranslation( translation );     mat3 mr = makerotation( r );      mat3 ms = makescale( 1.0/scale );       //transform     vec3 newcoord = vec3(v_texcoord.xy,1.0);                     newcoord = mt*newcoord;      newcoord = mr*ms*vec3(newcoord.x - 0.5, newcoord.y - 0.5,0.0) + vec3(0.5, 0.5, 0.0);      gl_fragcolor = texture2d(s_texture, vec2(newcoord.x, newcoord.y) );  }

the result is: result1
can see, result incorrect.

so, apply ratio of rectangle size texcoord.y:

//transform float fy = 0.5*(1.0 - size.y*1.0/size.x); newcoord.y = (newcoord.y-0.5)*size.y/size.x+fy; newcoord = mt*newcoord; \n" newcoord = mr*ms*vec3(newcoord.x - 0.5, newcoord.y - 0.5,0.0) + vec3(0.5, 0.5, 0.0); newcoord.y = (newcoord.y+0.5)*size.x/size.y-fy;

what i've got: result rectangle correct, position of center point incorrect.

so, how right result? thanks.

here origin texture： origin texture

getting right order of operations important.

when receive texture coordinates, in range [0, 1]. however, need translate them, in [-0.5, 0.5], before rotate them, rotating around center of texture. apply scale, , translation.


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