Android triangle is drawn in the vertex shader is as follows:
attribute vec4 vPosition;
void main() {
gl_Position = vPosition;
}
vPosition vertex, passed by the application.
Fragment shader code is as follows:
precision mediump float;
void main()
{
gl_FragColor = vec4(1,0,0,1);
}
Create a program:
private fun createProgram() {
var vertexCode =
AssetsUtils.readAssetsTxt(
context = context,
filePath = "glsl/triangle_vertex.glsl"
)
var fragmentCode =
AssetsUtils.readAssetsTxt(
context = context,
filePath = "glsl/triangle_fragment.glsl"
)
mProgramHandle = GLTools.createAndLinkProgram(vertexCode, fragmentCode)
}
triangle_vertex.glsl vertex shader and triangle_vertex.glsl represent a fragment shader and files stored at assets / glsl directory, readAssetsTxt assets directory common method to read the file.
Get a handle parameters:
vPositionLoc = GLES20.glGetAttribLocation(mProgramHandle, "vPosition")
Vertex data initialization line code is as follows:
var vertexBuffer = GLTools.array2Buffer(
floatArrayOf(
0.0f, 0.5f, 0.0f, // top
-0.5f, -0.5f, 0.0f, // bottom left
0.5f, -0.5f, 0.0f // bottom right
)
)
draw:
override fun onDrawFrame(p0: GL10?) {
GLES20.glUseProgram(mProgramHandle)
vertexBuffer.position(0)
GLES20.glEnableVertexAttribArray(vPositionLoc)
GLES20.glVertexAttribPointer(vPositionLoc, 3, GLES20.GL_FLOAT, false, 0, vertexBuffer)
GLES20.glDrawArrays(GLES20.GL_TRIANGLES, 0, 3)
}
GL_TRIANGLES representation drawing triangles.
Drawing triangle there are 3 ways:
- GL_TRIANGLES: 3 vertices drawing a triangle, the apex of the triangle, even if repeated, should also be declared in the vertex array. If there are six vertices, then a triangle composed of 2,3, 4,5,6 to form a triangle.
- GL_TRIANGLE_STRIP: two front vertices of a triangle, and a subsequent vertices of a triangle Further, if there are six vertices, the composition has a vertex of a triangle (1,2,3), (2,3,4), ( 3,4,5), (4,5,6) a total of four triangles, so there are N vertices, the triangle is drawn with a number N-2.
- GL_TRIANGLE_FAN: a first point to the central point, the other vertices as an edge point of the fan to draw the composition of adjacent triangles, if there are six vertices, vertex of a triangle with a composition (2,3), (1,3, 4), (1,4,5), (1,5,6) a total of four triangles.
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