How to crop texture by angle using OpenGL in Android?

Question

I have texture with semicircle. It should grow clockwise depending on given angle. First, my drawing function prepares vertex and texcoords buffers. Next, it loads rotation matrix and finally texture is drawn. Code looks something like this:

float[] vertexBuffer = {x0, y0, x1, y0, x0, y1, x1, y1};
float[] texCoordBuffer = {0, 0, 1, 0, 0, 1, 1, 1};
float[] matrix = getRotationMatrix(angle); // in Z axis
matrix[12] = (x0 + x1) / 2;
matrix[13] = (y0 + y1) / 2;

gl.glMatrixMode(GL11.GL_MODELVIEW);
gl.glLoadIdentity();
gl.glLoadMatrixf(matrix, 0);            

gl.glBindTexture(GL11.GL_TEXTURE_2D, m_TextureID[0]);

gl.glColor4f(1f,1f,1f,1f);
gl.glVertexPointer(2, GL11.GL_FLOAT, 0, vertexBuffer);
gl.glTexCoordPointer(2, GL11.GL_FLOAT, 0, texCoordBuffer);
gl.glDrawArrays(GL11.GL_TRIANGLE_STRIP, 0, 4);

I don't have any idea how to crop rotated texture and rotate it back. What is proper way to achieve such effect?

solidpixel solidpixel · Accepted Answer · 2016-11-24T10:23:49

Cropping in GL is basic rectangles, so not going to help here. If you want arbitrary angles you need to change your geometry and texture coordinates on the fly.

How to crop texture by angle using OpenGL in Android?

1 Answers