I have created a basic shader program to brush up on my openGL GLSL.
on the cpu side i have properly created my shader program .vp and .fp linked properly and error checked
my result when i render is always a black Triangle
Right before i link my program but after i attach both shaders i do this
glBindAttribLocation( program, 0, "vVertexPos" );
glBindAttribLocation( program, 1, "vColor" );
both my position variables and my color variable in the shaders
all of this is just a quick run through so im not worried about ugly code besides the openGL calls and shader setup
struct PosColVertex
{
float pos[3];
float color[4];
};
PosColVertex verts[3];
float vPos1[3] = { 0.5f, 0.0f, -1.0f };
float vPos2[3] = { 0.0f, 1.0f, -1.0f };
float vPos3[3] = { -0.5f, 0.0f, -1.0f };
memcpy( verts[0].pos, vPos1, sizeof(float)*3 );
memcpy( verts[1].pos, vPos2, sizeof(float)*3 );
memcpy( verts[2].pos, vPos3, sizeof(float)*3 );
float vColor1[4] = { 1.0f, 0.0f, 0.0f, 1.0f };
float vColor2[4] = { 0.0f, 1.0f, 0.0f, 1.0f };
float vColor3[4] = { 0.0f, 0.0f, 1.0f, 1.0f };
memcpy( verts[0].color, vColor1, sizeof(float)*4 );
memcpy( verts[1].color, vColor2, sizeof(float)*4 );
memcpy( verts[2].color, vColor3, sizeof(float)*4 );
glGenBuffers( 1, &vboHandle );
glBindBuffer( GL_ARRAY_BUFFER, vboHandle );
glBufferData( GL_ARRAY_BUFFER, sizeof(PosColVertex)*3, verts, GL_DYNAMIC_READ );
for my rendering this is what i do
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT );
//use our shader program
glUseProgram( program );
//set which vertices we will be using
glBindBuffer( GL_ARRAY_BUFFER, vboHandle );
glEnableVertexAttribArray( 0 );
glEnableVertexAttribArray( 1 );
//specify our vertex attribute
glVertexAttribPointer( 0, 3, GL_FLOAT, GL_FALSE, sizeof( PosColVertex ), (void*)(0) );
//specify our texture attribute
glVertexAttribPointer( 1, 4, GL_FLOAT, GL_FALSE, sizeof( PosColVertex ), (void*)(12) );
glPushMatrix();
//draw our rectangle
glDrawArrays( GL_TRIANGLES, 0, 3 );
glPopMatrix();
glDisableVertexAttribArray( 0 );
glDisableVertexAttribArray( 1 );
did i do something wrong with the glVertexAttribPointer calls? i've checked my shader it works and it does change the values since i hard coded values in there before to test it. but im assuming im not telling openGL on the CPU side how to read my verts properly. any help?
tri.vp
#version 330
in vec3 vVertexPos;
void main(void)
{
gl_Position = vec4( vVertexPos.x, vVertexPos.y, vVertexPos.z, 1 );
}
tri.fp
#version 330
out vec4 vFragColor;
in vec4 vColor;
void main(void)
{
vFragColor = vColor;
}
GL_DYNAMIC_READ
for your buffer object usage? Are you planning to read the memory back to the CPU? Do you plan to update the memory? If not, useGL_STATIC_DRAW
. – Nicol Bolas