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this blog from: http://stackoverflow.com/questions/13745334/understanding-shader-mat4-vec4-calculation

understanding shader mat4 * vec4 calculation

can someone confirm following calculation, please? :)

in normal android opengl shader the computation:

mat4 a; vec3 p;vec3 pos = (a * vec4(p,1.0)).xyz;

would be calculated like this:

pos.x = a0 * p.x + a1 * p.y + a2 * p.z + a3 * 1.0; pos.y = a4 * p.x + a5 * p.y + a6 * p.z + a7 * 1.0; pos.z = a8 * p.x + a9 * p.y + a10 * p.z + a11 * 1.0;

is this correct? or did I miss something? every help is highly appreciated.

answer1:

Ok actually I've found a reliable source: http://www.khronos.org/files/opengles_shading_language.pdf

vec3 v, u; mat3 m;

And

u = m * v;

is equivalent to

u.x = m[0].x * v.x ?+ ?m[1].x * v.y ?+ ?m[2].x * v.z; u.y = m[0].y * v.x ?+ ?m[1].y * v.y ?+ ?m[2].y * v.z; u.z = m[0].z * v.x ?+ ?m[1].z * v.y ?+ ?m[2].z * v.z;

Therefore

vec3 v, u; mat4 m;

And

u = (mat * vec4(v,1.0)).xyz

should be equivalent to

u.x = m[0].x * v.x ?+ ?m[1].x * v.y ?+ ?m[2].x * v.z + m[3].x * 1; u.y = m[0].y * v.x ?+ ?m[1].y * v.y ?+ ?m[2].y * v.z + m[3].y * 1; u.z = m[0].z * v.x ?+ ?m[1].z * v.y ?+ ?m[2].z * v.z + m[3].z * 1;

Please correct me if I'm wrong though.

轉載于:https://my.oschina.net/aspirs/blog/612475

超強干貨來襲 云風專訪：近40年碼齡，通宵達旦的技術人生

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