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OpenGL Vertex Shader Runtime Issues (not using VBOs or textures)
uniform mat4 uMVP;
attribute vec4 aPosition;
attribute vec4 aNormal;
attribute vec2 aTexCoord;
varying vec2 vTexCoord;
varying vec4 vPrimaryColor;
void main() {
  gl_Position = uMVP * aPosition;
  vPrimaryColor = vec4(1.0, 1.0, 1.0, 1.0);
  vTexCoord = aTexCoord;
}

uniform sampler2D sTex;
varying vec2 vTexCoord;
varying vec4 vPrimaryColor;
void main() {
  gl_FragColor = vec4(0.0, 1.0, 0.0, 1.0);
}

// Load the matrix
glUniformMatrix4fv(gvMVPHandle, 1, false, &mvPMatrix.matrix[0][0]);

// Draw the square to be textured
glVertexAttribPointer(gvPositionHandle, 2, GL_FLOAT, GL_FALSE, 0, gFullScreenQuad);
glEnableVertexAttribArray(gvPositionHandle);
glVertexAttribPointer(gvTexCoordHandle, 2, GL_FLOAT, GL_FALSE, 0, gFullScreenQuad);
glDrawArrays(GL_QUADS, 0, 4);

const GLfloat PlotWidget::gFullScreenQuad[] = { -1.0f, -1.0f, -1.0f, 1.0f, 1.0f, 1.0f, 1.0f, -1.0f};

vTexCoord = aTexCoord;

vTexCoord = vec2(1.0, 1.0);

glVertexAttribPointer(gvPositionHandle, 2, GL_FLOAT, GL_FALSE, 0, gFullScreenQuad);
glEnableVertexAttribArray(gvPositionHandle);
glVertexAttribPointer(gvTexCoordHandle, 2, GL_FLOAT, GL_FALSE, 0, gFullScreenQuad);
glEnableVertexAttribArray(gvTexCoordHandle);
glDrawArrays(GL_QUADS, 0, 4);